The US was not "late" in joining the war. Washington and other early leaders warned strongly against getting involved in foreign wars, and Europe had a long string of wars from the 1700s through 1914. The Franco-Prussian War, The Crimean War, the Russo-Japanese War, etc., were wars between European powers, and the US wisely did not choose sides or take part. Through most of its history, the US military and economy were not really capable of competing with European powers. That lesson was learned fully in the War of 1812, when British forces burned Washington.
Only after the Civil War did the US military become truly powerful. Prior to that, our military was aimed mainly at keeping unruly Indian tribes down, with one war against Mexico. After the Civil War, the US Navy became more powerful, and the US did take on one fading European power in the Spanish American War. But in general, the US population wanted nothing to do with European wars.
When WW1 broke out, the opinion of Americans was strongly divided. Many German-Americans supported the Kaiser's army, many French and British-Americans supported the Allies, and most Americans wanted to stay out of the war. There was no strong American political or economic interest to get involved. Wilson was actually re-elected with the slogan "He Kept US Out Of War."
America watched in horror as the trench warfare settled into a stalemate, and the age of chemical warfare began. Even after German Uboats sunk the Lusitania, killing hundreds of Americans, most people wanted to stay out. As Wilson began to realize the war was stalemated, he decided to move the country toward war. He is quoted as saying that if the allies won, the US foreign policy toward Europe would remain the same because the French and English were enlightened democracies or constitutional monarchies. Germany had a stronger autocratic government, and American policies would have to be changed dramatically if they won the war.
So, the US was not late entering the war, but had to be put in a situation in which their interests were threatened before they decided to go to war.