Complex sentence: During the early 1900s the Boulonnais were imported in large numbers to the United States, and were quite popular in France; the European population suffered severe decreases during 20th century wars.
Split into simpler sentences: During the early 1900' s, the Boulonnais were imported in large numbers to the United States and were quite popular in France. The European population suffered severe decreases during 20th century wars.