Answer:
In the years leading up to 1898, the United States maintained a strict policy when it came to foreign policy, alliances, and foreign entanglements - a policy of neutrality in which kept the United States out of global conflicts. This was suggested by President George Washington in his farewell address, and further cemented by President James Monroe in his statement known as the Monroe Doctrine.
In 1898, the United States emerged on the world stage when it entered the Spanish American War in Cuba. The participation of the United States in this conflict was caused by many events including yellow jornalism, a tactic used by journalists to sway the American public in favor of war, and by the sinking of the ship _USS Maine in Havana Harbor.
Following American victory in the war, the United States annexed the following colonies from Spain: Puerto Rico, Guam, and the Philippines. The idea of American imperialism, or establishing American colonies overseas, was debated in both government and the American public. Senator Henry Cabot Lodge was strongly against American isolation.
America extended its influence over the Western Hemisphere by building the Panama Canal in the early 1900’s under President Taft. The project was seen as a major need for the US Navy, and American economy.
After the early foreign interventions of the United States, it became clear to President Roosevelt that the Monroe Doctrine had to be amended. As such, he wrote an addition known as the Roosevelt Corollary. This stated that European empires had to restrict their influence in North America, and that the United States had the right to exercise a police power to guarantee peace. This was also called the Good Neighbor policy.
By 1914, the world was at war. European empires were battling across Europe for dominance in colonization and military power. Under the first term of President Woodrow Wilson, the United States maintained neutrality in the war. This changed after a series of events including the sinking of the ship Lusitania, and the Zimmerman Telegram, which suggested that Germany and Mexico would form an alliance against the United States.
When the United States entered the war, it joined the alliance known as the Allies. The United States had a small military in 1917 when it declared war, and had to hold a draft to create an army large and strong enough for war.
The war had many effects on the United States many more women had to secure employment in factories. African Americans migrated to the north and western cities of the United States both for work and to escape racism and Jim Crow laws in the south. Additionally, there became a widespread fear of immigrants - this movement was known as the Nativism.
Finally, after Allied victory in World War 1 - the overwhelming opinion of Americans was that they wished to return to the foreign policy of Neutrality. As such, President Wilson’s plan for the peacekeeping entity known as the League of Nations was not popular and the Treaty of Versailles was not ratified.