They are not Trots, they were a flavor of German Communists specifically from the KPD if I am remembering my acronyms correctly.

Anyways, to summarize, while they were in theory allied with the Soviet Union, Rosa Luxembourg argued against, for example, giving Ukrainians their own nation, as they didn’t actually have a distinct ethnic identity outside of recent nationalist romanticism, whereas Lenin and Stalin believed that allying with the Ukrainian nationalists and giving them their own nation after the revolution, would allow them a more united front against their actual enemies in international capital and the white army. Stalin, especially, being a minority Georgian, was early on very big on the idea of giving persecuted ethnicities within the Russian empire latitude to form their own nations, ultimately compromising with others in the Bolsheviks with his idea to literally split up most of Russia into local nations.

In hindsight, Luxembourg may have been correct, but it literally took the collapse of the Soviet project to see her visions of ethnic conflict fulfilled. Yet with the fall of Yugoslavia, we also saw what could have been the eventuality of her ideas as well. It turns out that the national problem is really really difficult.

There are plenty of other theoretical differences as well, but I am not going to bore you with the details here.