Complex sentence: Large scale immigration of Chinese laborers began after the Opium Wars the Burlingame Treaty with the United States in 1868 effectively lifted any restrictions on immigration and began large-scale immigration to the United States.
Split into simpler sentences: Large scale immigration of Chinese laborers began after the Opium Wars. The Burlingame Treaty with the United States in 1868 effectively lifted any restrictions on immigration and began large-scale immigration to the United States.