Were natural resources a primary reason for invading Romania during the middle ages-present?

The statement that the Romanian area was "invaded" many times is hard to contradict. All territories have been more or less "invaded", but taking a look at this area of Europe we cannot avoid the impression that here we are dealing with a higher scale of the phenomenon.

The general impression comes from the reasons stated in another answer which brings forth the fact that the Eurasian Steppe that starts east of Romania was a highway for invasions by migratory peoples since antiquity. It's not that Romanian polities were attacked by armies coming from that highway of invasions, but that they couldn't even exist before that highway was cut off by modern medieval powers.

The original "Indo-Europeans" came on the same route probably, followed by Sarmatians, Scythians, then Huns, Goths and all the other "invaders" of the post-Roman and early medieval Europe.

We know of the Dacian kingdom and of its "invasion" by the Roman empire, which plays a big role in the Romanian narrative discussed in the question above. But that narrative largely ignores the fact that Dacia was mostly an unstable area, only exceptionally and for short periods unified or pacified. It was permanently under pressure from the east, and most of the time the origin of invasions into the Roman empire by multiple peoples more or less "migratory" and more or less allied or mixed with the "Dacians". Stopping those invasions was one of the main reasons why the Romans invaded Dacia.

Interestingly for our topic, one of the other main reasons of the Roman conquest of Dacia (meaning mainly Transylvania) was indeed natural resources, especially the gold of the Transylvanian mountains.

The other main reason was the power of the Dacian state (the only independent kingdom in Europe other than the Romans at that time). But that power depended on the cooperation with the peoples of the steppe and on the integration of those peoples (and of those peoples' cultural and especially military structures) within the Dacian power-structure. This is characteristic for the eastern European states: like the Goths in western Europe, some migratory peoples have created powerful kingdoms in eastern Europe. And of these some have become a bulwark against new invasions from the east, like Bulgarians and Hungarians.

It is the Hungarian kingdom that decisively put a stop to the Mongol threat from the east, and thus stabilized the region enough that the first Romanian larger polities emerged in the 14th century. (That's something which the patriotic narrative is happy to ignore. Instead it puts forward the fact that in this process the Hungarians had themselves "invaded" those very territories - beside the fact that they were "invaders" in the first place etc...)

The peoples of the steppe do not count for much in the invasions of Romanian lands after 1300, and the power-struggle between larger adversaries that crossed their interests on that area becomes the main factor of instability and "invasion": since their political beginnings (and up until the present, given that Moldavia is still separated between two states across spheres of influence, and that part of its territory is occupied by Russian troupes) Wallachia and Moldavia found themselves at the frontiers of conflict between much more powerful states which periodically invaded the territory: first Hungary and the Mongol (until c 1400), then Hungary, Poland and the Ottomans (until Mohacs, 1526), then Russia, Austria, and the Ottoman (until the Crimean War that pushed those war frontiers to the east and led to Romanian independence in the 19th century).

How much resources counted in all this? Not decisively, anyway, but they counted of course, as they always do.

Hungarian king's occupation of Transylvania had something to do with the same gold that the Romans coveted, but the political reasons were far more important (not to mention the fact that Transylvania was not "Romanian" when the Hungarians invaded it). The Ottoman exploited the two principalities as much as they could, but there was not much to exploit in the first place and the ottoman capacity to exploit economically was limited: here too, the reason for repeated military interventions were political - part of an expansionist logic and the resulting wars with the other powers -, not economical.

Once the Romanian states became vassal the Ottoman became interested in stability, but that was hard to get for the aforementioned motives. Interestingly enough - and contrary to the patriotic narrative - Ottoman political and economic pressure forced centralization of the state (especially) in Wallachia and the development of fiscal and economical institutions which weren't there before (as Marian Coman shows) and would serve exploitation of resources. Later they became a sort of "fiscal farms" which the Ottoman were trying to develop and stabilize. But the exploitation was an effect, not a cause of the initial "invasion".

Romania was invaded again during WW1 and WW2, but it must be noted that in WW1 it attacked and "invaded" Transylvania first, before being overwhelmed and occupied by Germany, while in WW2 it went east along with the invading Germans up to Stalingrad, before being occupied by the USSR.

It has to be emphasized though that Romanian alliance with Hitler's Germany was the result of a political and territorial "invasion" through the Ribbentrop-Molotov pact, which resulted in the brutal bullying of Romania into the Nazi camp. A main purpose of Nazi policy concerning Romania was access to Romanian oil - and against that access were directed the US and UK raids against Romania.

As a summary answer to the question "Were natural resources a primary reason for invading Romania":

Mostly NO.

No, or not especially, because although invasion and occupation is bound to involve exploitation of resources, in most cases that was not the primary reason in the case of Romanian area, excepting the case of migratory invaders from the steppe who moved and "invaded" as a matter of course for cultural as well as economic reasons (they lacked many resources which they were used to steal from others). But those powerful warriors have bothered more the Dacians and Romans than Romanians because they were mostly neutralized before the Romanian principalities could emerge.

YES, partially, in two cases:

• the Roman invasion of Dacia had gold as one of the main reasons, although the ancient techniques allowed exploitation only up until 215. (But Dacia is not "Romania".)

• Hitler's "expansion" towards Romania (the territorial loss suffered by Romania through the Ribbentrop-Molotov pact) was related to access to Romanian oil. But that was not really an invasion, the oil was paid, and Romania was supposed to get territorial compensation to the east.

Even in these two cases exploitation of natural resources is subordinated to other causes. Geopolitical reasons of war actions on Romanian lands far outmatch the economic ones.

I believe Romania's chief misfortune during the Middle Ages was to be right next to Eurasian Steppe, in an era when settled communities really had no military answer to the expert horse archers that steppe country naturally incubated.

Another view (for as long as the link lasts)

To make matters worse, right on the other side of Romania is the Hungarian Plain (or Alföld), which was also perfect territory for those same pastoralists. One can imagine that in the middle in their way was not a fun place to be.

So in a way, yes Romania did contain valuable "resources", if you count good pasture land as a resource where militarily potent pastoralists are concerned.