السلام عليكم ورحمة الله وبركاته
When Islam started, It wasnt untill there came an order from Allah for Prophet Muhammed PBUH to urge his followers to fight for the cause of Islam..
Jihâd[] (holy fighting in Allâh's Cause) is ordained for you (Muslims) though you dislike it, and it may be that you dislike a thing which is good for you and that you like a thing which is bad for you. Allâh knows but you do not know. (2:216)
Because of that we have to fight in order to spread islam and defend our religion and our countries.. BUT, we cant start a war just by ourselves. Only a leader can start a war by ordering his army or urging citizens of his country to fight for him for the favor of puplic interest or for the cause of Islam..
Then fight (O Muhammad SAW) in the Cause of Allâh, you are not tasked (held responsible) except for yourself, and incite the believers (to fight along with you), it may be that Allâh will restrain the evil might of the disbelievers. And Allâh is Stronger in Might and Stronger in punishing. (4:84)
O Prophet (Muhammad SAW)! Urge the believers to fight. If there are twenty steadfast persons amongst you, they will overcome two hundred, and if there be a hundred steadfast persons they will overcome a thousand of those who disbelieve, because they (the disbelievers) are people who do not understand. (8:65) Now Allâh has lightened your (task), for He knows that there is weakness in you. So if there are of you a hundred steadfast persons, they shall overcome two hundreds, and if there are a thousand of you, they shall overcome two thousand with the Leave of Allâh. And Allâh is with As-Sâbirûn (the patient). (8:66)
And since our Muslim leaders find no reason for us to go into war, then there is nothing we can do.. even if we see otherwise.
And fight in the Way of Allâh[] those who fight you, but transgress not the limits. Truly, Allâh likes not the transgressors. [This Verse is the first one that was revealed in connection with Jihâd, but it was supplemented by another (V.9:36)]. (2:190) And kill them wherever you find them, and turn them out from where they have turned you out. And Al-Fitnah[] is worse than killing. And fight not with them at Al-Masjid-Al-Harâm (the sanctuary at Makkah),[] unless they (first) fight you there. But if they attack you, then kill them. Such is the recompense of the disbelievers. (2:191) But if they cease, then Allâh is Oft-Forgiving, Most Merciful. (2:192) 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).[] But if they cease, let there be no transgression except against Az-Zâlimûn (the polytheists, and wrong-doers.) (2:193)
Hope this answers your questions..