God appointed those apostles and disciples .... So man didn't save himself from anything. It was all divine power granted from God. And yeah the crusades and everything were bad .... Mistakes made by fallible man .... Who can and will chose to work in his own accord and try and be his own boss ... Which leads to failure and greater sin like the examples you mentioned. Anyone can say they are Christian and are doing the work of God when in reality are working from their own accord and are not doing the will of God.