Since the 19th century there have been the two opposing socialist groups: the internationalistic movement (marxists), and the nationalistic movement (various names, including fascists and nationalist socialists - i.e. nazi's). They tend to hate each others guts with a vengeance. Because they appeal to exactly the same voters!

They mainly differ in two respects: 1) the marxists want socialism to embrace the whole planet, so that there is only one country, whereas the fascists are perfectly happy to realise socialism in the country, where they are. And 2) the marxists don't just want de facto private ownership of the means of production erased, but also the nominal private ownership. The fascists can accept nominal private ownership, for as long as the actual control over the means of production is in the hands of the government.

Big differences, seen from their viewpoints. But pretty small to everybody else.