Complex sentence: The dominion arose during the Livonian War, when the northern parts of present-day Estonia (Reval (Tallinn) and the counties of Harjumaa, Western Virumaa, Raplamaa and Järvamaa) submitted to the Swedish king in 1561, and Läänemaa in 1581.
Split into simpler sentences: The dominion arose when the northern parts of present-day Estonia were united under Swedish rule in 1561. The city of Reval and the counties of Harjumaa, Western Virumaa, Raplamaa and Järvamaa surrendered in 1561, and Läänemaa was conquered in 1581.