Christians participating in wars and massacring people?

These events happened a few years ago, but reading about that struck me a bit, since I am surrounded by Christian people who say that Christians are not involved in these matters, since the use of weapons is obviously not the right thing to do, and less kill. This event caught my attention.

It starts like this:
The Party of the Lebanese Phalanges is a political party of the extreme right of Lebanon, most of its members and social support comes from the Maronite Church, the largest Christian denomination in the country. In 1982, when the Palestinians fled to Lebanon and massacred a large number of Christians and members of the Lebanese Falange party as leader at that time, Bashir Gemayel; the massacre was dominated as "the massacre of Damour". In response to the massacre, the Lebanese party of Christian origin massacred the Palestinians who lived in the refugee camps in Western Beirut during the 1982 Lebanon War and the massacre was guarded by the Israeli Defense Forces (IDF) that controlled the departure and the entrances to the refugee camp This massacre was called "Massacre of Sabra and Shatila".

Personally, I am a Christian and these events leave me a lot to talk about and I believe that if you have to fight for a "just" cause and your ideals, you have to fight. On the other hand, I do not accept that inocent people are massacred for any reason or ideals, it is not the same to fight to defend your nation than to kill with security. The origin of the murder was to get revenge, but unfortunately the innocent people had to pay and that should not be accepted. What do you think of these events?