This dissertation argues Boston merchant Alfred Robinson played a key role in the transition of California from a Mexican province to part of the U.S. His life and writings provide a window into what he described as the U.S. “colonization” of California. Although California historians have written about Robinson’s 1829-1847 career as a hide and tallow merchant, no one has yet captured the full range of his influence, showing how he helped facilitate the imperial ambitions of the U.S. This study builds on recent literature that suggests commercial activity not only preceded, but influenced the U.S. conquest of California. Robinson believed a racial, religious, and economic transformation was underway across the world, and that he was a part of it. To this end he created drawings and wrote newspaper articles, essays, books and poetry. Through the end of his life he helped consolidate the U.S. conquest and settlement of Alta California, though he began to publicly critique its results just a few years before his death in 1895. Drawing primarily on Robinson’s personal correspondence, this study demonstrates connections between biography, U.S. History, and world history, showing their interrelationship in nineteenth-century California.