After the sinking of the Lusitania by Kaiser Wilhelm's Germany U-boats in 1915, public opinion changed and the United States entered World War I on APRIL 6, 1917.
Soon, Americans were arriving in Europe at the rate of 10,000 a day to fight "the Hun."
George M. Cohen wrote the popular song, "Over There," for which he was awarded a Congressional Gold Medal by President Roosevelt in 1936:

Over there, over there,
Send the word, send the word over there
That the Yanks are coming, the Yanks are coming
The drums rum-tumming everywhere.
So prepare, say a prayer,
Send the word, send the word to beware -
We'll be over, we're coming over,
And we won't come back till it's over, over there.
Within two years, America enlisted 4 million soldiers and spent 35 billion dollars.
On April 16, 1917, President Woodrow Wilson encouraged ministers:
"This is the time for America...I hope that the clergymen will not think the theme of it an unworthy or inappropriate subject of comment and homily from their pulpits."
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Prayers and Presidents-Inspiring Faith from Leaders of the PastIn an Executive Order to the Army and Navy, January 20, 1918, President Woodrow Wilson stated:
"The President, commander in chief of the Army and Navy...enjoins the orderly observance of the Sabbath by the officers and men in the military and naval service of the United States.
The importance for man and beast of the prescribed weekly rest, the sacred rights of Christian soldiers and sailors, a becoming deference to the best sentiment of a Christian people, and a due regard for the Divine Will demand that Sunday labor in the Army and Navy be reduced to the measure of strict necessity."
On May 11, 1918, President Woodrow Wilson issued a Proclamation of a
National Day of Fasting:
"It being the duty peculiarly incumbent in a time of war humbly and devoutly to acknowledge our dependence on Almighty God and to implore His aid and protection..
.a day of public humiliation, prayer and fasting...be observed by the people of the United States with religious solemnity
and the offering of fervent supplications to Almighty God for the safety and welfare of our cause, His blessings on our arms, and a speedy restoration of an honorable and lasting peace to the nations of the earth...
Therefore, I, Woodrow Wilson, President of the United States of America, do hereby proclaim...do exhort my fellow-citizens of all faiths and creeds to assemble on that day in their several places of worship and there, as well as in their homes, to pray Almighty God that He may forgive our sins...
and to purpose only those righteous acts and judgments which are in conformity with His will; beseeching Him that He will give victory to our armies as they fight for freedom."
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