A religious believer might not go to war because their religion is against hurting anyone, killing anyone and making people suffer.
Just war is:
-Legal
-Happens for a reasonable cause
-Civillians must not be used
Holy war is war which happens for religious purposes, for example if Muslims and Christians were fighting over holy land- that would be holy war.
Holy wars usually have three elements:the achievement of a religious goalauthorised by a religious leadera spiritual reward for those who take partAn example of holy war are the Crusades
References: BBC Bitesize
They didn't. At the time that Jesus lived the Romans had very little dealings with him. In fact they didn't even know who he was. That's why when it came time to arrest Jesus they had to have someone (Judas) point him out. It was only a certain group of Jewish authorities who perceived Jesus as a threat and so acted against him.