The statement that correctly compares the differences between Ethiopia's and Siam's resistance to imperialism is:
Ethiopia was forced to resort to violent resistance to maintain independence, while Siam used diplomacy.
Ethiopia successfully resisted imperialism through military engagements, most notably during the Battle of Adwa in 1896 against Italy, while Siam (now Thailand) effectively navigated the pressures of imperialism through a series of diplomatic agreements and reforms, maintaining its sovereignty.