Complex sentence: During the period 1815-1849 an autonomous Polish region linked with Prussia had been formed and was abolished after 1849, but the Poles achieved independence in 1918-1919 (refer to "Greater Poland through history" section below).
Split into simpler sentences: During the period 1815-1849 an autonomous Polish region linked with Prussia had been formed. The Poles regained independence in 1918-1919 (refer to "Greater Poland through history" section below).