See here the present >> Distribution of European Y-DNA haplogroups by country in percentage
Thus most important components are:
1] I =33% original and dominant hplgr -trachians, dacians – geti, rumini;
2] R1a=17.5% – ‘kurgan’, scytian, ‘slav’ component on second place;
3] J=15% middle est, farming infusion – anatolians, ‘greeks’
4] E1b1b=15% ‘african’, ilyr – albanians, egyptians
5]R1b=12% western europe hplgr – celts
1] Last Ice Age: The last glaciation in Europe began some 120 000 years ago, being coldest about 20‐18 000 years ago, when the ice covered the Europe to approximately 50N. Most Europe is covered by ice or tundra, the Black Sea is a lake, there is continuous land between Balkans, ‘Greek Islands’ and ‘Turkey’. 3 small pockets of human resistance remain, on of them in Balkans, with an I2 population!
2] Spread of farming in Europe – first mixtures – farming was introduced by migrations of people from Middle East with J2 haplogroup (anatolians).
The result after this first migration is the following. The original I population in Romania melted the J2 population, present J percentage in Romania is 15%. In Europe highest J percentages can be found in Cyprus 43%, Crete 39%, Sicily 26.5%, Anatolia 33%
From Caucaz came the caucasians – G population, the shepards, present G percentage in Romania is 5%. G is highest in Gagauzes population 13.5%, high in Anatolia 11%, Cantabria 10.5%, Tatar 11%, Sardinia 12%, S-Italy 10.5%, Central Italy 11%, Crete 9.5%, Austria!, Tyrol, Corsica, Provence 7.5%. Present T percentage is only 0.5% in Ro, relatively high percentages of T can be found in South Greece, Auvergne and Malta – 4.5%, South of Italy, Anatolia 2.5%, South of Spain 2%. Most of Europe is ”blue”, western europe is mostly I populations (Tardenoisioan Culture), practically no R1b in Europe, R1a present only in the North of the Black Sea (Bug-Dniester Culture – Kurgan).
3] 4000-3500 BCE, most of Old Europe, is pretty much I2 population with significant J mixture and some small G percentage. However ‘the afrikans’, the E-V13 populations are advancing in the West of the Balkans – future ilyrian / albanian populations, related to Egypt, to African populations. Present day percentage of E1b1 in Romania is 15%, another big wave melted in the original basic I2 population. Biggest E percentages in Europe can be found today in Kosovo 47.5%!, Central Greece 29.5%, Albania 27.5%, Bulgaria 23.5%, Montenegro 27%, Macedonia 21.5%, Bosnia 23%, Galicia 22%, Ile de France, Sicily 20.5%,
Transylvania is the LINK between Danube Culture = Linear Pottery and the famous Vinca (SW), Boian/Hamagia (SE) & Cucuteni (E) cultures!
4] Present R1b percentage in Romania is 12%. The R1b epic saga begins around 2800-2500BCE. Again Transylvania is the central stage, the first celtic area and the link between Balkans (Old Europe), Western Europe still mostly I2 – the Megalithic Cultures and NE of Europe, the kurgan R1a Corded Ware Culture. I am saying – ‘Latin languages’ have I origin, most future ‘latin’ areas, Romania, France and Spain were originally areas inhabited mainly by populations with I2 haplogroups, before the arrival of the R1b celts. I guess that the celts were able to impose themselves in Western Europe as dominant haplogroup and not in the lower Danube area, because of the higher density in Old Europe, from here started the repopulation of Europe, here were the best living conditions for the most of the time, here was the biggest human reservoir of Europe. As Herodotus used to say, the Thracians were the biggest population of Europe, outnumbered in the world only by Indians. The biggest rivers always all over the world produced the biggest populations and the biggest cultures (Egypt/Nile, India/Ganges, Middle Asia/Euphrates, Europe/Danube).
2500-2000 – Conquest of Western Europe by R1b! R1a Corded Ware Culture in North Germany, Poland, Ukrajna and Russia. The R1b celts conquered Europe from E to W but later they migrated back East, to Transylvania, Balkans and Anatolia. Ancient Galatia (/ɡəˈleɪʃə/; Greek: Γαλατία) was an area in the highlands of central Anatolia (Ankara, Çorum, Yozgat Province) in modern Turkey. Galatia was named for the immigrant Gauls from Thrace (cf. Tylis), who settled here and became its ruling caste in the 3rd century BC, following the Gallic invasion of the Balkans in 279 BC. It has been called the “Gallia” of the East, Roman writers calling its inhabitants Galli (Gauls or Celts).
wiki: Celts in Transylvania > The appearance of Celts in Transylvania can be traced to the later La Tène period (c. 4th century BC). Excavation of the great La Tène necropolis at Apahida, Cluj County, by S. Kovacs at the turn of the 20th century revealed the first evidence of Celtic culture in Romania. The Celts exercised politico-military rule over Transylvania between the 4th and 2nd century BC and brought with them a more advanced iron-working technology. They were also responsible for the spread of the potter’s wheel into a much wider area than the one they occupied.
Large areas of ancient Dacia populated early in the First Iron Age by Thracian people were affected by a massive migration of (R1a) Scythians moving east to west during the first half of the first millennium BC. They were followed by a second equally large wave of Celts migrating west to east. Celts arrived in northwestern Transylvania in around 400–350 BC as part of their great migration eastwards. When Celtic warriors first penetrated these territories, the group seem to have merged with the domestic population of early Dacians and assimilated many Hallstatt cultural traditions.
The second half of the 4th century BC saw the Middle La Tène Celtic culture emerge in north-western and central Dacia, a development reflected especially in burials of the period. Celtic artifacts dating to this time have been discovered at Turdaş, Haţegand Mediaş in modern day Romania. By 1976 the number of Celtic sites found in Transylvania had reached about 150, indicating a significant La Tène population surpassed only by the Dacians. These sites are mostly cemeteries. Archaeological investigations have highlighted several warrior graves with military equipment, suggesting that an elite Celtic military force penetrated the region. Celtic vestiges are found concentrated in the Transylvanian plateau and plain, as well as the upper Someş basin, whereas the surrounding valleys of Haţeg, Hunedoara, Făgăraş, Bârsa, Sf. Gheorghe and Ciuc have neither necropoleis nor settlements but only tombs or isolated items. This indicates that Celts occupied the territory between Mureş and Someş, west of the Apuseni Mountains, and the plains and plateau in the intra-Carpathian space along with the valley in the upper basin of Someş. Nevertheless, these valleys as well as those of Banat and Maramureş have also yielded contemporary Dacian findings. Of the Celtic cemeteries excavated the most important are those in Ciumeşti and Pişcolt (Satu Mare County) and Fântânele (Bistriţa-Năsăud County). These contain over 150 graves compared to the average of 50–70. Necropoleis have also been found at Sanislău (Satu Mare County), Curtuişeni (Bihor County), Galaţii Bistriţei (Bistriţa-Năsăud County), and Braşov (Braşov County).
In Transylvania, the Celts shifted from inhumation to cremation, either through natural progression or because of Dacian influence. Almost without exception, the necropoleis so far studied are bi-ritual, although cremation appears to be more prevalent than inhumation. The Celts in Dacia certainly cremated their dead from the second La Tène period onwards but Celtic inhumations appear no older than pit-grave cremations in any of the cemeteries. It is impossible to say whether the Celts turned away from the practice of cremation as the Scythians had. Although less frequent, inhumation still occurred as a constant practice even during the final stage of Celtic inhabitation of this territory. Celtic settlements had a rural character with such sites found in Mediaș, Moreşti, (Mureş County) and Ciumeşti.
Expansion of Celtic groups in the area may be related to their invasion of the Balkans around 335 BC, when a massive colonization of the Tisa plain and theTransylvanian Plateau occurred following the death of Lysimachus. However, the eastward movement of the Celts into Transylvania used a different route from the one taken by the hordes that attacked the Balkans. Celts did not occupy all intra-Carpathian areas of Transylvania, stopping short of the Maramureş Depression for instance, where excavations have uncovered Dacian fortifications from the 4th and 3rd centuries BC. As regards Celtic influence on local Daco-Getic culture, Vasile Pârvan has stated that the latter is wholly indebted to Celtic traditions and that the “La Tene-ization” of these northern Tracians was a cultural phenomenon primarily due to the Celtic population who settled the area. 
Archaeological sites of the 3rd and 2nd centuries BC reveal a pattern of co-existence and fusion between the bearers of La Tène culture and the indigenous Dacians. Domestic dwellings exhibit a mixture of Celtic and Dacian pottery while several Celtic graves contain Dacian type vessels. At Celtic sites in Dacia, finds show that the native population imitated Celtic art forms that they admired, but remained firmly and fundamentally Dacian in their culture. Dacian archaeological finds in the Transylvania area increase in number from the middle of the 2nd century BC.
During the first half of the 2nd century BC, Pompeius Trogus writes in his Historiae Philippicae of a Dacian king, Oroles, who fought against Celtic incursions. Oroles is recorded as resisting the intrusion of the Bastarnae, a people now generally considered to be of Germanic origin but who were in fact Celto-Germanic and, according to Livy, spoke a Celtic language.The Bastarnae moved from Silesia into what is now central and northern Moldavia. Pompeius Trogus along with Justin also record the rise in Dacian authority prior to 168 BC under the leadership of King Rubobostes. Around 150 BC, La Tène material disappears from the area concurrent with ancient writings which mention the rise of Dacian authority. This ended Celtic domination and it is possible that the Celts were forced out of Dacia. On the other hand, some scholars have posited that the Transylvanian Celts remained but merged with the local culture and thereafter ceased to be distinctive. The boundary between the Celts and Dacians near the River Tisa is depicted in 2nd century BC pottery found at Pecica in Arad County, a prosperous trading center at the confluence of the two peoples.
A classic period of Geto-Dacian La Tène culture began in the 1st century BC centered around the city of Sarmizegetusa Regia in south-western Transylvania. Dacian king Burebista defeated the Celtic Boii and Taurisci tribes between 60–59 BC. However, some archaeological finds in Dacian settlements and fortifications feature imported Celtic vessels and others made by Dacian potters imitating Celtic prototypes. These discoveries in sites from regions north and west of Transylvania show that relations between the Dacians and the Celts continued in the period 1st century BC-1st century AD. During Burebista’s time the Dacians became closer to the remaining Celtic populations than they had been when the Celts ruled Transylvania. Evidence from the earlier period shows Celtic burials and settlements with only occasional Dacian elements while Dacian settlements with Celtic finds are infrequent. This situation reversed after Burebista’s conquest when a distinctive hybrid Celtic-Dacian culture emerged on the Hungarian plain and in the Slovakian regions. Most of the Celts were melted into the Geto-Dacian population and contributed to Dacian cultural development. These Celtic tribes, who were skilled in iron exploitation and processing, also introduced the potter’s wheel to the area, thereby contributing to acceleration of the development of Dacia. By this time, prosperous Celtic communities had spread over the whole territory of modern Romania.
So original ‘Dacian’ populations melted the R1b invaders, and the fusion between the old Dacians and the La Tene celts produced the main classical Dacian Culture starting with the Dacian Empire of Burebista than finishing with the Dacian kingdom conquered by the Roman Empire / Trajan.
It is interesting to see in 800AD a situation in Europe pretty much replicating much of situation we can see above in Europe, in the time of Burebista, 900 years before Charlemagne. The Carolingian Empire goes on the footsteps of the old Celtic territories, the ‘Bulgarian Vlah’ Empire covers the Dacian+Thracian area, while the Southern Slavs occupy the Ilyrian area.
So we could say that in Romania we have a 10k or 7.000years I continuity, with a main basic I2 population which melted wave after wave, J, E, R1b and R1a populations.
5] The absorption of R1a populations was done in many thousands of year, there were many many waves coming over Romania from the East, most of them along the Black Sea shores. Present day R1a percentage in Romania is 17.5%. First wave was the Kurgan invasion that probably distroyed the Cucuteni Culture.
en.wikipedia.org/wiki/Kurgan_hypothesis#Kurgan_culture > Kurgan IV or Pit Grave culture, first half of the 3rd millennium BC, encompassing the entire steppe region from the Ural to Romania. There were three successive proposed “waves” of expansion:
- Wave 1, predating Kurgan I, expansion from the lower Volga to the Dnieper, leading to coexistence of Kurgan I and the Cucuteni-Trypillian culture. Repercussions of the migrations extend as far as the Balkans and along theDanube to the Vinča culture in Serbia and Lengyel culture in Hungary.
- Wave 2, mid 4th millennium BC, originating in the Maykop culture and resulting in advances of “kurganized” hybrid cultures into northern Europe around 3000 BC (Globular Amphora culture, Baden culture, and ultimately Corded Ware culture). According to Gimbutas this corresponds to the first intrusion of Indo-European languages into western and northern Europe.
- Wave 3, 3000–2800 BC, expansion of the Pit Grave culture beyond the steppes, with the appearance of the characteristic pit graves as far as the areas of modern Romania,Bulgaria, eastern Hungary and Georgia, coincident with the end of the Cucuteni-Trypillian culture and Trialeti culture in Georgia (c.2750 BC).
en.wikipedia.org/wiki/Usatovo_culture > The Usatovo culture, 3500—3000 BC, is an archaeological culture facing the Black Sea between the mouths of the Bug River and the Danube in present-day Romania, Moldavia, and southern Ukraine. It is seen as a hybrid, with roots in both the Cernavodă and the Tripolye cultures, overlain by an intrusive steppe-derived element of the presumably Indo-European-speaking Kurgan culture.
Than of course followed the scytians/sarmatians who were mentioned as inhabiting large areas in the central Eurasian steppes starting with the 7th century BC up until the 4th century AD. And finally the Slaves From the early 6th century AD.