What was the backbone of the american economy in the 1920

What kind of contact did christopher columbus and native americans initially have?

(05.04 mc) how did the roman transportation system keep the empire strong? plz

Which statement about submarine use in world war i is true? the allies never found a way to counter german submarine warfare. germany’s use of submarines affected the united states’ decision to enter the war. only the germans used submarines in world war i.