Why did the United States enter World War I, and what
impact did the war have on the nation?

The U.S. entered World War I because Germany embarked on a deadly gamble. Germany sank many American merchant ships around the British Isles which prompted the American entry into the war. World War one had huge effects on America including highly productive industry that preceded the Great Depression, jobs given to woman, which helped pass the nineteenth amendment, and a new kind of diplomacy and antiwar sentiment that affected America's entrance into World War II.

answer: the time zones used to be whatever the local authority wanted them to be. one town might have 6am whenever the sun came up and another town had 6am 10 minutes later.  

the trains had a hard time when their orders said to be at a certain point at 6am.  

6am, but who's 6am.  

the railroads got together and set the time zones more or less along the longitude lines across the country.

explanation:

copernicus finished the first manuscript of his book, "de revolutionibus orbium coelestium" ("on the revolutions of the heavenly spheres") in 1532. in it, copernicus established that the planets orbited the sun rather than the earth. he laid out his model of the solar system and the path of the planets.