Complex sentence: After 1837, however, he devoted himself principaUy to the study of American colonial history, and in order to have access to the records of the early Dutch settlements in America he obtained in 1839 an appointment as attach of the American legation at the Hague.
Split into simpler sentences: After 1837, however, he devoted himself principally to the study of American colonial history. In order to have access to the records of the early Dutch settlements in America, he obtained, in 1839, an appointment as attaché of the American legation at the Hague.