Answer: C. The German invasion of Russia
Step-by-step explanation:
President Wilson's in this speech was calling for German soldiers to leave the territories of Russia that it had captured and acquired by the Treaty of Brest-Litovsk.
Russia had joined the war to support the allies and most especially Serbia but were overrun by the superior efficiency of the Germans who pushed very far into their territories and in the subsequent peace negotiations, demanded a lot of land. Wilson was asking for Germany to leave that land.