Islam treats non-muslims unequaly. They are forced (by higher goverment or representative of islam such as a Imam or ruler) to pick one of three options. Convert to islam, Pay a special taxtation (Jizya), or war (fight them).
Having war as an option is enough to render the peace claim wrong.
If Islam is not a religion of peace, then no organized monotheistic religion is. There is a common rhetoric of violence and subjugation in the majority of their religious scriptures.
Wars initiated by Muslims throughout the history were almost exclusively against the oppressor. It is not logically accepted to be peaceful with the oppressor. And these wars, do not count against peace. It is very clear in the Quran that, whenever peace is proposed, Muslims should accept it.
Compared to almost all other major groups (religious and nonreligious), the history of Muslims is almost completely clean of genocides. And be careful to not mix groups which are disguising as Muslims. The criteria is simple, if they have the Quran and the Sunnah the only sources of law.
If Islam was not a religion of peace, we will never see other religious minorities in any Muslim country. Jewish, Christians, pagans, .... they all live peacefully in the Muslim countries till now.