Islam means submission, more specifically, it is a religion of submitting to God's will.
Unjust violence is not in accordance with God's will, and sitting around doing nothing when your people are being killed is also not submitting to God's will.
Islam is a religion and way of life which can be understood from the Qur'an, which is the word of God Himself. From that, you can understand what you want to know about Islam. The Qur'an presents to you what type of god God is, and how you should worship Him.
Over and over again, the Qur'an commands the reader to be good, to forbid evil and indecency, to treat parents, relatives, neighbors, and the poor with kindness. To be friendly with those people who do not believe in your belief, and to defend yourself against those who attack you first. To not start hostilities, to avoid violence at all costs, and to be just in all matters, even if you have to go against yourself or your loved ones.
Once you know what the Qur'an teaches and commands, it's not difficult to realize what submission to God is all about.