A person's world view is the overall perspective from which he or she views and interprets the world. It can also include the beliefs about life and the universe held by a group (such as a "Christian world view"). The concept is from a German word, Weltanschauung.
A person's or a group's world view encompasses values, goals, concepts of the future, definitions of truth, etc. Naturally, you can see how differing world views have caused much conflict historically.
For example, the Nazi world view caused them to believe they were acting in the name of a higher ideal and in accordance with their world theory. They believed the Germans were the "Master Race" and because of this, it was their duty to eliminate any threats to that race, which in their twisted logic, included the Jews, handicapped, homosexuals, etc. Perceived by the rest of the world that did not share this world view, their acts were considered barbarism and evil and a violation of human rights.
Radical Islam's world view is that the world's problems are caused by secularism. They believe a solution is to establish Sharia law, and that anyone that interferes with their goals is evil. Therefore, they can justify holy war to eliminate threats to these goals (this is an over-simplification and there is much debate about this). Note that "radical" Islam is a huge departure from Islam itself.
In the Christian world view, everything is seen through the eyes of faith. Christians believe that the earth is not their home, but they are on earth for a purpose, and that purpose is to serve the God that sacrificed himself for them so that they can have eternal life. They believe that God made humans stewards of the earth, so Christians have the obligation to take care of the earth. They also believe that it is their duty to share the good news about eternal life with all people because this is what their loving God expects.
Other religious world views also believe their religion is the only true religion, so adherents of these faiths often become overzealous about sharing their faith because they are passionate about wanting others to have the peace that they have.