They didn't have to. On 11 December 1941, Germany declared war on the United States and immediately started attacking US shipping.
Any country can declare war on anybody else. What matters is can you back it up?
an act of terrorism
1917
The United States was bombed by the Japanese at Pearl Harbor which cause a declaration of war but Germany had an alliance with Japan and it had forced the United States to declare war on Germany too. Then Germany had an alliance with Italy which cause the United States to declare war on yet another country. Then the world was at war and therefore World War 2 started.
Great Britian
it caused Serbia to declare war on Austria Hungary
it caused Serbia to declare war on austria hungary
The US did not declare war on Germany. Germany declared war on the US shortly after the Japanese attack on Hawaii.
In both.
This is a really odd question as it assumes that most historians give bogus dates for the start of World War 2 in Europe.
No.
no
germany
Any country can declare war on anybody else. What matters is can you back it up?
Austria-Hungary.
Pearl Harbour.
yes