The Muslims have to pay taxes (which is 2.5 percent of their annual income) under the name of "Zakah" to provide welfare to the poor and the needy citizens; from both Muslims and non-Muslims. The poor and the needy (such as the Orphans, Widows and the disabled) from the Muslims are exempt from paying taxes.
The non-Muslims had to pay a varrying amount under the name of "Jizyah", depending on their situation, which is taxes that don't go to help poor and needy Muslims, but instead, it goes to the government to (1) Provide protection for them since they are a minority; (2) Provide means for them to practice their religions freely by building Temples or Churches for them.
As I mentioned above for the non-Muslims, there are exemptions for the poor, for females and children. The idea that Islam expanded by forcing people to convert by imposing jizyah is false simply because:
1) If they became muslim they would have to pay more in zakah
2) The poor and needy did not need to become muslim because as mentioned they would be exempt from paying jizyah