The United States Congress officially recognized the end of World War I when it passed a concurrent resolution on June 4, 1926, with these words:
Whereas the 11th of November 1918, marked the cessation of the most destructive, sanguinary, and far reaching war in human annals and the resumption by the people of the United States of peaceful relations with other nations, which we hope may never again be severed, and Whereas it is fitting that the recurring anniversary of this date should be commemorated with thanksgiving and prayer and exercises designed to perpetuate peace through good will and mutual understanding between nations; and Whereas the legislatures of twenty-seven of our States have already declared November 11 to be a legal holiday: Therefore be it Resolved by the Senate (the House of Representatives concurring), that the President of the United States is requested to issue a proclamation calling upon the officials to display the flag of the United States on all Government buildings on November 11 and inviting the people of the United States to observe the day in schools and churches, or other suitable places, with appropriate ceremonies of friendly relations with all other peoples.
An Act (52 Stat. 351; 5 U. S. Code, Sec. 87a) approved May 13, 1938, made the 11th of November in each year a legal holiday—a day to be dedicated to the cause of world peace and to be thereafter celebrated and known as "Armistice Day."
Reference: https://www.va.gov/opa/vetsday/vetdayhistory.asp