Obviously saying 'nothing' is a bit much, but it is true that colonialism brought materially higher civilisation. Prior to European arrival, the pre-Columbian cultures only had very limited use of metals like bronze or iron and largely lacked the wheel outside of child's toys. This is especially noteworthy when they built great Civilisations in Meso-America and the Andes.
In the continental US, their societies were mostly small villages practicing subsistance agriculture or hunter-gatherers - barring the odd exception like the Iroquois confederation. The arrival of European diseases went a long way to wiping out much of what there was, but to think that pre-Columbian America would always remain hermetically sealed from such pathogens is laughable.
European rulers often undertook infrastructure and such that no native ever would have done, or had the ability to. This is true even in Africa and India. For instance, Indian railways are extensive and were built early in the history of rail, because of the Raj - and the former Princely States today have a disadvantage here precisely because they were protectorates and not directly-ruled.
Without European colonisation, we would likely see a mostly empty land, or they would have to substantially Westernise anyway like Japan or China did. Good analogies would be the parts of Africa that were lightly colonised, mostly just straddling a few large railway lines or the like, such as Cameroon.
There was nothing in France before Rome took it over.
And yes, there was much more after Rome in France than in prior Gaul. While there were Oppida, these were mostly hillforts with competing tribes in low-level warfare. The Romans built large roads, trade and agriculture exploded, and built cities down on the plains. The Roman was a materially higher civilisation by any measure, and they promptly stopped Gallic human sacrifice and head-hunting. Colonisation can be messy and brutal, but the end result is often putting more there rather than less. In similar vein, sometimes it is good that the prior culture is destroyed if morally repugnant - an argument I would make of the Gauls as much as the Aztecs.
The world is not a Disney Pocahontas movie.