With that constraint gone, landscape painting developed. The Dutch were expertly skilled at it and influenced most of the rest of Europe.
But (with a couple of very interesting exceptions) we are talking about pastoral paintings here. Often very good ones (or at least better than the dire stuff churned out in the 18th century. It is difficult to emphasise enough quite how bad most 18th century art is) but an idealised representation of well-settled countryside all the same. And certainly not immune from what would later be called nationalism (particularly in the case of Dutch artists).
Ah, but I never said that all Romanticism was
good My point is that there was a major change in aesthetic perspective beginning at around about the beginning of the 19th century, and that the catalyst for this change was pretty clearly the Romantic movement. It's the movement's main legacy. An interesting feature of that change, incidentally, is that many of the consequences of it weren't properly felt until after Romanticism basically petered out in most fields after 1848.
Including, of course, landscape painting.