Complex sentence: When Uzbek Khan and Muhammad Shaybani besieged Kandahar, Babur found his nascent Kingdom of Kabul in danger, he felt that Kabul would be the next target of the Uzbeks.
Split into simpler sentences: When Uzbek Khan and Muhammad Shaybani surrounded Kandahar, Babur found his developing Kingdom of Kabul in danger. He feared that Kabul would be the next target of the Uzbeks.