The second decade became a time of scientific study in both the US and abroad. The discovery of superconductivity came in 1911, followed by the theory of continental drift in 1912, and the Black Hole Theory of 1916. Important warfare discoveries were made in 1915, when chemical warfare was used effectively by the Germans on Poland and in 1917 with the development of sonar. The most important event in these years, however, was World War I. The US became  involved in the war in 1917, when Germany violated an international law, which would endanger neutral
vessels.Under the Select Service Act the army grew from just 135,000 to 3 million. Ninety-three combat divisions were organized and thirty had combat service. At home supplies and money were raised through community support. The war ended when all involved parties met in Paris in 1919.
The construction of the  Panama canal was finally finished in 1914, after 7 treacherous years. Thanks to Henry Ford, thousands of jobs were provided at his motor company assembly line. This
new method of car manufacturing doubled the number of cars produced, and increased the company profits from $30 million in 1914, to $60 million in 1916. The new method had its disadvantages though, workers got tired of doing the same thing everyday. To deal with this problem, Ford increased wages from $2.50 to $5.
William Taft continued his presidency until 1912, when Woodrow Wilson, the former president of Princeton University and a New Jersey and governor of New Jersey. He was reelected in 1917. Unfortunately, in 1919, the last year of the decade, former President Teddy Roosevelt died peacefully in his sleep.
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