Fight those who believe not in God and the Last Day and do not forbid what God and His Messenger have forbidden -- such men as practise not the religion of truth, being of those who have been given the Book -- until they pay the tribute out of hand and have been humbled.
Koran 9:29
However, one often hears the argument that the Muslims don't generally believe in the violent verses of the Koran apply any more (which is a good thing).
That said, it would be interesting to see whether the future violence at the hands of 'The Messiah' that is described below is similarly denied by the Muslim posters here. I somehow doubt it.
Jesus’ second coming will be exceedingly violent. Ahadith describe the ultimate war with Christ, the conquering commander who judges and "breaks the crosses". It’s going to be bloody and gory. All pigs will be slaughtered and Jews annihilated. His followers have no compassion upon their enemies, many will be forced to embrace Islam. Jesus will conquer his enemies completely and Allah will consign them to having their flesh burnt off and re-grown in an endless cycle for all eternity.
It is an error to say that God never supports a war. Jesus is not a pacifist.
Relevant ahadith:
The Prophet said: There is no prophet between me and him, that is, Jesus. He will descent (sic) (to the earth)… He will break the cross, kill swine, and abolish jizyah. Allah will perish all religions except Islam.
Sunan Abu Dawud, Book 37, Number 4310, Narrated by Abu Hurayrah: see also Sahih Bukhari Volume 3, Book 43, Number 656
The Prophet (pbuh) said: There is no prophet between me and him, that is, Jesus (pbuh). He will descend (to the earth)... He will fight the people for the cause of Islam. He will break the cross, kill swine, and abolish jizya. Allah will perish all religions except Islam. He will destroy the Antichrist and will live on the earth for forty years and then he will die. The Muslims will pray over him.
Sunan Abu Dawud Book 37, Number 4310:
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: The last hour would not come unless the Muslims will fight against the Jews and the Muslims would kill them until the Jews would hide themselves behind a stone or a tree and a stone or a tree would say: Muslim, or the servant of Allah, there is a Jew behind me; come and kill him; but the tree Gharqad would not say, for it is the tree of the Jews.
Sahih Muslim 6985