Washington warned to not get involved in foreign matters and to follow the policy of isolationism, to avoid European powers because America wasn't really strong and big at that time. So involving in European matters could result in controlling the USA however they wanted and getting the USA involved in European conflicts. USA didn't follow Washington's advice and later on got involved in WWI and WWII. If they didn't they could've focused on improving domestic matters rather than wasting money in warfare.
The answer that best describes how African Americans participated in the war effort during World War II is letter B. They were fully integrated into the armed forces and fought alongside whites. They actually volunteered to join
