There are two types of Jihad (fighting/striving in the Cause of Allah): "Jihad Talab (Initiative Jihad)" and "Jihad Daf'(Defensive Jihad)." Both types have the same goal, namely, conveying the Din (Religion) of Allah, calling people to it, bringing them out of the darkness into the light, making Allah's Din reign on earth, and making all and every kind of worship purely for Allah Alone.
And fight them until there is no more Fitnah (disbelief and worshipping of others along with Allâh) and (all and every kind of) worship is for Allâh (Alone).
And fight them until there is no more Fitnah (disbelief and polytheism, i.e. worshipping others besides Allâh) and the religion (worship) will all be for Allâh Alone [in the whole of the world].
Then when the Sacred Months (the 1st, 7th, 11th, and 12th months of the Islâmic calendar) have passed, then kill the Mushrikûn (See V.2:105) wherever you find them, and capture them and besiege them, and lie in wait for them in each and every ambush. But if they repent and perform As Salât (IqâmatasSalât), and give Zakât, then leave their way free. Verily, Allâh is OftForgiving, Most Merciful.
"I have been commanded to fight the people so that (the purpose of fighting) they testify that there is no deity but Allah and that Muhammad is the Messenger of Allah, and they perform Salah (Prayer) and pay Zakah (obligatory charity). Anyone who does this has protected from me their blood and property, unless by right of Islam, and their account will be with Allah."
(Agreed upon as Sahih (Authentic) by AlBukhari and Muslim from a Hadith on the authority of Ibn 'Umar [may Allah be pleased with them])