Amazon.com description: Product Description: The United States didn't expand from the 13 original states to its present size all at once. Many different events took place to shape the country into what it is today. Readers explore the details behind many of these events, including the purchase of Alaska and the signing of the Treaty of Guadalupe Hidalgo. These essential social studies curriculum topics are introduced in a clear and engaging way. Carefully chosen primary sources and other historical images allow readers to immerse themselves in this important period of U.S. expansion.