How Khwarazm was captured by Gaznavids and why?

Ghaznavids during the thirty two years of sultan Mahmouds rule (388- 421A.H) Followed an expansionism policy. Many campain and incursion that conducted under name of Gazveh and Jihad brought them a lot of wealth and trophies. These materials and trophies all together brought them more power and reputation and credibility. Accordingly they were known as largest Islamic empire in the East of Islamic caliphate. One of the most important and wealthy territory in Khorasan which after its conguest provided them more reputation income and wealth was kharzam, that in this time was ruled by Al-mannids this region came under control of ghaznavids in 408 AH. Since the eapture of the province was one of the most important events of Sultan Mahmud Kingdom, this article based on sources that period, it is going to review the political and economic reasons that Mahmud campained againt Kharazm and how he could captured it and what was the result of it.