Complex sentence: It was signed into law on March 11,1941, a year and a half after the outbreak of World War II in Europe in September 1939 but nine months before the U.S. entered the war in December 1941.
Split into simpler sentences: It was signed into law on March 11,1941, a year and a half after the outbreak of World War II in Europe in September 1939. This was nine months before the U.S. entered the war in December 1941.