Complex sentence: After Finland's independence followed strained relations with Sweden in connection with the Finnish Civil War and the Åland crisis, and the attitudes to the language issue sharpened to become a prominent feature of domestic politics during the 1920s and 1930s.
Split into simpler sentences: After Finland's independence, relations with Sweden became strained in connection with the Finnish Civil War and the Åland crisis. The language issue sharpened to become a prominent feature of domestic politics during the 1920s and 1930s.