The challenges that the nation faced after the Civil War was money
It is actually D. Citizens in ancient Greek city states developed ideas about representation that established direct democracy -Apex
Answer
The war officially ended with the February 2, 1848, signing in Mexico of the Treaty of Guadalupe Hidalgo. The treaty added an additional 525,000 square miles to United States territory, including the land that makes up all or parts of present-day Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming. Mexico also gave up all claims to Texas and recognized the Rio Grande as America’s southern boundary. In return, the United States paid Mexico $15 million and agreed to settle all claims of U.S. citizens against Mexico.
https://www.history.com/topics/mexican-american-war/treaty-of-guadalupe-hidalgo#section_2
Fossils give information of the lifestyle of past flora and fauna
