Why did Korea and japan choose a policy of isolationism?

Why did the german kingdoms unite into one nation of germany?

What was gained through the gadsden purchase

How does the supremacy clause of the u.s. constitution affect the states? o a. it requires each state to establish a supreme court. b. it declares that the federal government can take away state powers if necessary. o c. it allows state governments to overthrow the federal government if necessary. o d. it ensures that the u.s. constitution overrules each state constitution