Answer:
The real and main reason was The Assassination of Archduke Francisco Ferdinand heir to the throne of Austria-Hungary in his visit in Bosnia. The Hero Gavrilo Princep killed him because he want his country to have independence.
There are also reasons like Imperialism, Nationalism, Militarism and many otherd
The policy of promoting industry in the U.S. by adoption of a high protective tariff and of developing internal improvements by the federal government.
I think it was 1865 which is d pls give me brainliest answer