Many did convert to Islam. This is how Islam built it's empires. Islam didn't merely want to conquer nations and leave cultures intact and the religions to the conquered people. They wanted to convert all to Islam. Dar-el-Islam. Houes of Islam = peace according to Islam.
if what are you saying is right i will give you some questions
if many converted to Islam ,why did they?
islam don't force one to be amoslem, so they won't be killed
you will say they pay the tax so they still on their religion
most of that nations were under the control of the Persian or roman empire
which forced this nations to pay a heavy taxes
when moslems take the control they canceled all that taxes for all people
also is that tax payed by all non moslems??
no, it is just payed by youth who are able to work and work so if he cant pay he won't pay
so no women or children or old people or even monks or handicapped pay it
how mush was it?
1 dinar in the year
why was it ?
was it just because you are not moslem
no it was for youth instead of serving at the army and to be under the protection of the islamic army
so that tax helped to the fast spread of islam,because every nation waited for moslems to come
for example after 5 years of moslems entering to Egypt,the Romans back and invade egypt and control on the capital alexanderia
even non moslems sent to khalifa asking him for help and pleasing him to sent an army as fast as he can
also that tax wasn't an islamic invention
for example jesues in the bible say give what for ceasr to ceasr and what for god to god
you can find western books speak about that like
adam metz in his book islamic civilization
will diorant in his book story of civilization