This document collection looks at the decades leading up to the U.S. war with Mexico from multiple perspectives. Students will engage with a wide range of primary sources, constructing an argument based on the central question: What does the contest for lands at the U.S. border with Mexico reveal about America's imperialist ambitions? Students are guided in their analyses of the documents by a learning objective, central question, historical background, source headnotes, source questions, project questions and suggestions for further research. By analyzing texts and images with such different perspectives, students will gain an understanding of how historians interpret, assess, and contextualize primary sources. This unit will also add to students' understanding of the present in a historically based context.