After the death of Spitamenes and his marriage to Roxana (Roshanak in Bactrian) to cement his relations with his new Central Asian satrapies, Alexander was finally free to turn his attention to the Indian subcontinent. Alexander invited all the chieftains of the former satrapy of Gandhara, in the north of what is now Jhelum River, Pakistani region (Modern History) to come to him and submit to his authority. Omphis, ruler of Taxila, whose kingdom extended from the Indus to the Hydaspes, complied, but the chieftains of some hill clans, including the Aspasioi and Assakenoi sections of the Kambojas (known in Indian texts also as Ashvayanas and Ashvakayanas), refused to submit.
After Alexander defeated the last of the Achaemenid Empire's forces in 328 BC, he began a new campaign against the various Indian kings in 327 BC. He wanted to conquer the entire known world, which in Alexander's day, ended on the eastern end of India. Greeks of Alexander's day knew nothing of China or any other lands east of India. The Siege of the Sogdian Rock, a fortress located north of Bactria in Sogdiana, occurred in 327 BC.