You should know that asking those questions, in that way, will make people assume that you're here to start a fight. If you really want to learn about our ideas, don't start by challenging us to justify them.

We tend to not take concepts such as the self determination and territorial integrity of nation states very seriously, because nation states are constructs and as such don't really have rights. If you look at the conflicts in Palestine and Ukraine in detail, without these abstractions, they are very different situations. Essentially, the war in Ukraine is an escalation of an existing civil war within Ukraine between Ukrainians with Russian heritage and the government which was installed in a pro-US coup, while Israel is a ethnonationalist project to systematically remove Arabs from Palestine. The news mega will be able to give you much more information if you're prepared to ask nicely.

As far as alternatives to capitalism and how they scale, different people will have different answers because we're a cross-tendency site. Personally I would say that China is a market-socialist state and also the most populous country in the world. Compared to the US the Chinese state is clearly able to discipline the market and steer it to achieve social goals such as the elimination of extreme poverty. I think China's system represents a step forward towards communism.

Do stay for a while and figure things out. We're used to people coming here to pick fights though, so don't be that guy.