Question

Why were Japan and Italy unhappy with the results of the peace after WWI?

Answer 1

They did want to be imperial

Answer 2

Italy was left out of the majority of decisions that the Allied Powers made in the Treaty of Versailles, because Britain and France thought that Italy hadn't pulled much weight during the war despite being promised territorial gains. The Japanese were also excluded despite having aided Britain. So they wanted to get what they didn't in the first war, and evidently so did Germany, which is what led to WW2.