Complex sentence: In 44 BC when King Burebista of Dacia died and his kingdom began to collapse, the Iazyges began to take possession of the Pannonian Basin, the land between the Danube and the Tisa rivers (modern south central Hungary).
Split into simpler sentences: In 44 BC King Burebista of Dacia died and his kingdom began to collapse. After this the Iazyges began to take possession of the Pannonian Basin, the land between the Danube and the Tisa rivers (modern south central Hungary).