Complex sentence: The United States has had diplomatic representation in the nation of Germany and its predecessor nation, the Kingdom of Prussia, since 1835, with two breaks in relations (1917 to 1921,1941 to 1955), while Germany and the United States were at war.
Split into simpler sentences: The United States has had diplomatic relations with the nation of Germany and its predecessor nation, the Kingdom of Prussia, since 1835. These relations were broken twice (1917 to 1921,1941 to 1955) while Germany and the United States were at war.