In large measure, WW2 was caused by the Great Depression. People suffered and they elected dictators to solve their problems. The League of Nations was not effective in keeping the peace since the US was not a member. Now the US may withdraw from the UN and again people are hurting from the lingering effects of the Great Recession, which was really a depression for many. And again the people are electing would be dictators to positions of power. In the case of Donald Trump, we have a president who is ignorant of world affairs and who has surrounded himself with retired generals who want to impose our views on the world, by force if necessary.