Muslims: explain the whole slave thing?

[Darya]

according to history you can find anything your tendency desires.a muhammedian finds everything about muhammed right and positive. and the one against muhammed finds everything about him negative. therefor history is not something reliable because of different types of historians. for understanding this issue we should pay attention directly to the verses of quran. there are so many verses for some major sins to be forgiven, you should make free the slave e.g. 4:92 , 5:89 .besides the verse of 90:13 is consisted of two words <to release the slave>. the book is speaking of releasing the slaves around 1400 years ago while the human being has put aside it just recently. even in some regions the slavery isn`t revoked yet.