All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Al-Kharaaj has two meanings in the Sharee'ah, a general meaning and a special meaning.
1- General meaning: It is the money (wealth) which the Muslim state collects and spends according to the Sharee'ah.
2- Special meaning: It is the tax which the Muslim rule imposes on agricultural land.
The first person who imposed Al-Kharaaj (agricultural) land was ‘Umar Ibn Al-Khattaab during his caliphate after consultation with the Companions and other reliable persons.
When many conquests took place and the Muslim state became very large, 'Umar feared that the vast agricultural land will be abandoned, so he decided that it is better that this land is not divided among the conquerors; rather, it would remain as an endowment for all the Muslims, and so, he imposed a tax on whoever cultivates it, and the Muslim state would spend it on the general benefit of the Muslims, such as protecting borderline cities, providing water, paving roads and spending on orphans and widows.
By now, you would know the impact and effect of Al-Kharaaj in the state.
Allah knows best.