Why did the united states announce the open door policy? answers?

How did the united states surprise other delegates at the washington naval conference in 1921

Why did some states believe they had the power to overturn federal laws?

What role did mazzini play in italian unification? a.) he dreamed of a united italy and took the first steps to achieving it. b.) he conquered the southern part of italy, including sicily. c.) he was the first leader of a united italy. d.) he was assassinated by the french government, making him a martyr.