By the late 1800s, powerful interests pushed the United States to engage in a more active and imperialist foreign policy. Not least among these was the publishing industry. Hoping to sell papers with sensational headlines, William Randolph Hearst and Joseph Pulitzer were militating for involvement in the ongoing civil war in Cuba between Cuban nationalists and the Spanish government.

Furthermore, US companies had huge investments in Cuba and the instability was costing Americans money. In 1898, de Lôme’s letter was leaked. In it, a Spanish diplomat made slighting comments about President William McKinley, describing him as weak and primarily concerned with his own reputation. Shortly thereafter, the USS Maine, which was in Havana to protect Americans, if necessary, exploded. The US Naval Court of Inquiry determined that the explosion was caused by a mine (a later investigation suggested it was a fire that led to the explosion, not a hostile act). The US declared war. The war lasted about three months; in the negotiations that followed, the US acquired the Philippines, Guam, and Puerto Rico.

Moreover, the Platt Amendment was inserted into the Cuban constitution in 1901, allowing the US to intervene if the US professed to see any threat to Cuban independence. Although US imperialism was opposed by some, opportunities for profit carried the day. Theodore Roosevelt, McKinley’s successor, embraced the US’s aggressive foreign policy.

The Monroe Doctrine asserted that European nations had no right to colonize the Western Hemisphere; the Roosevelt Corollary added that the US would intervene as needed to insure stability in Latin America. Roosevelt’s motto was “speak softly and carry a big stick” — in other words, be diplomatic, but be prepared to use force. The force needed to exercise this policy was the Great White Fleet, a modern US navy. The Panama Canal affords an example of Big Stick diplomacy.

To get the land for the Canal, the US put military support behind an uprising by Panama (then part of Colombia). Grateful, the new Panamanian government granted the US permanent lease for the Canal Zone. President Taft moved to a less aggressive policy: “Dollar Diplomacy.”

In this strategy, the US used its wealth to support governments and governmental policies that benefited US interests or the interests of US countries. The US intervened in this way in the Caribbean, Nicaragua, China, and Liberia. The policy of Dollar Diplomacy was rejected by Woodrow Wilson. His “Moral Diplomacy” cloaked US interference in the politics of other nations as concern for the liberties of the citizens of those nations.

When World War I broke out in Europe, the United States tried to stay neutral but many Americans had a preference for Britain and were happy to continue manufacturing and selling goods to the Allies. However, Germany tested the US commitment to neutrality with the sinking of the Lusitania (1915), a passenger ship that carried many prominent US citizens as well as ammunition and shells destined for the war in Europe. The deaths of 128 Americans outraged the American people, but the US remained neutral. In 1916, the US began to expand its military preparedness.

Although after sinking the Lusitania, Germany had abandoned its aggressive submarine warfare, in 1917 it declared its intention to return to unrestricted submarine war. Also in 1917, the Zimmermann telegram came to light; in it, the Germans had suggested Mexico should enter an alliance with Germany and attack the United States. At last, the US entered the war.

During the war, unlike the US, Canada, which was still politically tied to the UK, was involved from the beginning. Approximately 60,000 Canadians died in the war and almost three times that number were wounded. Canadian factories, too, worked overtime to supply the needs of the war. The Canadian economy was stressed by the pressure of the war; prices rose, and some Canadians began to listen to critics of involvement such as Henri Bourassa.

Furthermore, by 1917, Canada had been forced to enact the Military Service Act to draft 100,000 more young men. Conscription was a divisive issue and attempts to enlist conscripts led to rioting, including the Quebec City Conscription Riots in March and April, 1918. When the war concluded in 1919, the US played an important role in the settlement negotiations.

Woodrow Wilson’s “14 points” included principles such as disarmament, self-determination, and the creation of an international peacekeeping organization. Wilson actively pushed for these principles and was able to achieve some of them. In particular, he won the creation of the League of Nations, which was incorporated in the Treaty of Versailles.

Back in the United States, politicians worried that signing the treaty and joining the League would inextricably bind the US to European politics, potentially dragging the US into future European wars. The stress of the political negotiations wore on Wilson and he eventually suffered a stroke; the US rejected and refused to ratify the Treaty of Versailles.

In the United States, the war had a profound impact. The US had prospered economically during the war. On the homefront, women had proven their importance and won the vote through the 19th Amendment (1920). African Americans had served gallantly, but in segregated units. They returned with desire to be treated more equally in civilian life. But, perhaps the biggest impact of the war, was the way it cemented in the minds of Americans the importance of neutrality. In Canada, the war had brought some similar changes. Its manufacturing had improved, for instance. Now, however, Canada looked more to the US as a diplomatic and economic partner than to Britain.