The allie power was mostly against Jermany and Austria-Hungary. But lets see how did each by each countries join the allie powers at ww1 participation
Japan
One of the reasons for Japan's participation in ww1 was that they saw a good opportunity in ww1 to have territorial gains as they were confident to join the Allies as there were very powerful countries in it . It also had allied with Uk which it didn't want to break by joining Central Power.