From about 1820 to its height in the early 1900s, the United States and Canada experienced a huge influx of people from other countries seeking to become citizens. This fascinating book details the historical evidence that helps explain why there was a mass migration of people from around the world. Readers will learn how prejudice and circumstances at the time of an event can influence people's interpretation of evidence, including items such as passports and other immigration documents, transportation tickets, engravings, photographs, paintings, and newspaper stories. Readers will learn how to use critical thinking in their own examinations of evidence. Present-day examples show how history repeats itself when evidence is denied or interpreted to one side's benefit. Teacher's guide available.