What is 1 major cause of international tensions in the 1900s?

In the 1900s, one major cause of international tensions came from holdings of (and access to) Natural Resources. Especially during the pre-war period, both the abundance and the lack of natural resources served as a cause of rising tension between nations on either side of the spectrum. Two examples may illustrate: for Germany, living space was deemed essential, and it sought to take such space from its neighbors. For Japan, oil was the key element, and it finally went to war to procure it.