How did European Americans imagine and assert their claims to western land? Objective 1. To determine and analyze the geographic and political forces that influenced control of New Mexico and the southwestern United States; 2. To examine the ways in which different groups asserted political and economic claims to the region; 3. To determine what role their own community played in westward expansion. Background Time Period: 1820s to 1865 Topics: This lesson could be used in American history, social studies, and geography courses in units on westward expansion or the Civil War. Preparation The s Duration: 90 Minutes.