100 years ago, war declaration started the ‘American Century’ - SFGate:
"...Then, 100 years ago Thursday, the United States declared war on Germany and, following victory in 1918, started what would eventually become known as the “American Century.”
President Woodrow Wilson won re-election in 1916 with the slogan “He has kept us out of war.” Another of his campaign catchphrases had a more contemporary ring: “America first.”
In Europe, both sides had dug in for trench warfare, relentless shelling and gas attacks in northern France and Belgium.
Some days there were tens of thousands of casualties in unprecedented carnage.
Despite outrage over German destruction and atrocities, it took until April 2, 1917 for Wilson to call for war in an address to Congress.
By then, millions had already died.
The U.S. entry changed everything.
“Why? There was a real deadlock,” said Professor Luc De Vos, a military historian from Leuven University in Belgium.
The arrival of up to 2.1 million U.S. troops became a big factor..."