France started the Panama Canal a long time before the U.S. took over the project with Colombia. Later, the United States encouraged Panama to break away from Colombia and gain independence. When the canal opened in 1914, it belonged to the U.S. However, President Jimmy Carter signed a treaty that gave the canal to Panama in 1999.
The Mexican Revolution began when Mexican President Francisco Madero was arrested after being in office for only a few months. Madero called for a revolution when the man who had him arrested, Porfirio Diaz became president.
The Spanish American War was started by Hearst and Pulitzer, newspaper owners, when they protested Spain's treatment of the Cubans in their newspapers. Spain lost spectacularly in the charge of the Rough Riders at San Juan Hill, and the United States won the war.
When Commodore Perry from the U.S. entered Tokyo Harbor, the Japanese were frightened because they had never seen such advanced ships. He came with a letter from President Millard Filmore to open up trade. Japan agreed a year later in the Treaty of Kanagawa when Perry came back a year later.
At the time the Opium War started, Britain had been selling opium, an addictive drug, to China. Beause Britain had banned opium in their own country, China was wondering why they were selling it in their country. This led to the Opium War, a war where the battles were mainly at sea. Britain won with ease and kept selling opium in China.
In 1823, U.S. President James Monroe issued the Monroe Doctrine, a document stating that no countries in the Americas were to be colonized by any European powers. This document was made because many of the countries in the Americas were new and weren't very stable at the moment.