I watched a documentary which basically claims that modern-day Romanians are not the descendants of Rome, but that the Romans and the Romanians share a common ancestor with the same language. One of their stronger arguments is that it's impossible for the Romanian language to become so latinized in the 150 years or so in which Rome occupied a small part of Romania (I think they said about 16%), because in other places where they occupied a much greater region (such as Egypt) the languages only show traces of Latin. What do you think, is this a good theory? There is also a part 2 in which they also show genetic evidence among other things, but I was not able to find a translated version of it. If you would like more detailed information from part 2, please let me know. Thanks.
I'm not a linguist so I can't comment on whether 150 years are enough or not to thoroughly Latinize a language. However, I think I can point out that the analogy with Egypt is deeply flawed.
When the Romans conquered Egypt from the Ptolemaic dynasty they took over a country that had roughly speaking two distinct populations: a "Greek" elite and semi-elite that was already Hellenized and spoke Greek and a native Egyptian population which spoke its own language and took no part in the political, cultural, administrative or financial affairs of their masters (except for the priests, but they were a thin layer which was probably as distant from the plain native folks as the foreign overlords).
With the advent or Roman rule nothing much changed for the Egyptian native peasant - he kept tilling his land, paying his taxes and had as little need or incentive to learn the language of his masters as before. Therefore, small wonder that his own language bears few traces of theirs.
Why was the linguistic situation different in other modern-day-Romance countries which the Romans conquered (such as France or Spain)? I think it's because in these countries the mass of native population had willy-nilly constant contact with the Romans and adopted eventually their language. A new elite grew up through trade and services to the Romans which associated itself with Latin. On the other hand, in Egypt there were no conditions for the rise of such an elite because there was little internal trade and the Romans did not settle the hinterland densely or required the direct services of the natives, having the "Greek" segment of the population at their beck and call.
So, to sum up, the comparison of Romania to Egypt is not a valid one.
P.S. There was a third major part of the Egyptian population at the time: the Jews. But for the purposes of this discussion this is not crucial so I left this fact out to keep matters simple.
The territory of the Republic of Moldova is for more than 200 years under strong Russian influence - political, economical, cultural, linguistic etc. But up till now there is no sign of assimilation of the indigenous Romanian-speaking population. If compared with the antiquity over the last 200 years there were much more "channels" for promoting the assimilation policy but the result is well known - the local population preserved its ethnic and linguistic identity. For this reason it is hard to believe that only 160 years of Roman presence in 16% of Dacian territory could lead to the latinization of the local population. From the other hand when speaking about partial Russification over the last 200 years we must distinguish two separate phenomena - the increased percentage of Russian native-speakers in the region and the "contamination" of the Romanian language of indigenous population. The local Romanian-speaking population borrowed a lot of Russian words which are used in daily communication, but the structure of the language did not change at all. The Russified Romanian language in Moldova is a Romanian language with plenty of Russian loan words but with intact grammar. The same phenomenon can be seen in Ukrainian villages in Moldova which are surrounded by Romanian villages. Sometimes they speak an Ukrainian language with so many Romanian insertions which is understood only by the members of that small community. The point is that for changing the language spoken in a region it is not enough to teach them another language. In the best(or worst) case they will borrow more or less words from the new language and will use them in their traditional language.
The question is to what degree the romance language speaking ancestors of the Modern Romanians in Transylvania, Moldavia, and Wallachia were descended from ancient Romanized Dacians and Roman colonists, and to what degree they were descended from Romance language speakers who arrived in the 3 Romanian regions from elsewhere sometime (probably over centuries) during the Middle Ages.
Those 2 possibilities are at the extreme and opposite ends of the spectrum of possible origins for the Romanians, and from what I have read Romania is deep enough into southeastern Europe that the supporters and defenders of those 2 extreme positions are often very violent supporters of their views.
So it is possible that some other persons who might answer later may shed more heat than light on the question due to their strong ethnic identification with one or the other extreme view.