It is jihad for those living under such oppression! However, it is not permissible for vigilantes to go there as there is no unified Muslim flag to fight under. Muslims must denounce these massacres and must assist their Muslim brothers there with money and all what is needed for them to defend themselves.
Muslims are not safe due to their sins and because Allah is testing them. If they follow the deen and apply Allah’s orders, Allah will give us victory.
The best thing for you and for the Muslims suffering, is to make du’aa for them and give out charity to help them.