US declared war on Germany because of the U-Boats attacking vessels. The Central Powers such as Germany, Austria-Hungary, and the Ottoman Empire declared war on the Allied Powers such as Great Britain, France, Russia, Italy, and Japan. While that was going on the the Triple Alliance such as Argentina, Brazil, and Uruguay were in war with the Triple Entente such as France, Russia, and Great Britain.
Because
After archduke Ferdinand was assassinated, Austria Hungary declared war on Serbia. Russia then came to Serbia's aid because of an alliance and declared war on Austria Hungary. Germany declared war on Russia because of its alliance with Austria Hungary. Britain declared war on Germany because of its alliance with Russia. Other countries such as France and the Ottoman Empire soon chose sides and World War 1 began
After Hitler Invaded Poland because Britan had a alliance with Poland
Russia.
Mobilized its military because of its alliance with Serbia.
Leaders knew that if they declared war, their allies had to join the fight with them.
leaders knew that if they declared war, their allies had to join the fight with them.
leaders knew that if they declared war, their allies had to join the fight with them.
Leaders knew that if they declared war, their allies had to join the fight with them.
leaders knew that if they declared war, their allies had to join the fight with them.
Following the attack on Pearl Harbor on December 7, 1941, the United States declared war on Japan. Because Germany and Japan were in an alliance, Germany then declared war on the US. The United States, in turn, declared war on Germany.
leaders knew that if they declared war, their allies had to join the fight with them.