False. Even before Ww2, European countries were still economically interdependent and yet still WW2 happened. What maintains peace is democratically elected leaders and separation of powers so that no single mad-man can ever singlehandedly turn a nation to war. That's why we had peace since WW2, democracy. Which Russia rever really had. So being dependent on countries with corrupt undemocratic governments where one leader can do whatever he feels like with no real opposition to stop him, was the real issue.
It depends, and it is often cultural. Iraq was peaceful for many years without real elections.
I think history has plenty of counter-examples. Interdependence also provides incentives for one to either take over or extort the other. Taiwan and mainland China are interdependent, and that situation is tense.
I think it's the other way around. If the relationships are already peaceful, then it's much safer to have interdependence. Think Canada/US, or the various countries within the EU.
I don’t claim that interdependence is sufficient for peace. It is much more complicated. So counter examples are to be expected. What I still believe though: Intentionally increasing interdependence makes war less likely not more.