Complex sentence: Changes in immigration laws in the United States in the 1920s, greatly restricted the number of immigrants allowed to enter, this led to a major reduction in the immigrant trade for the shipping lines, forcing them to cater for the tourist trade to survive.
Split into simpler sentences: Changes in immigration laws in the United States in the 1920s greatly restricted the number of immigrants allowed to enter. This led to a major reduction in the immigrant trade for the shipping lines, forcing them to cater for the tourist trade to survive.