how can you figh terrorism with war?

Not all war is terrorism. Terrorism by definition is the use of violence and intimidation n the pursuit of political aids while war is a state of armed conflict between different nations or states. Therefore a british citizen could set of a bomb in Britain and it would be terrorism not war. If a Scottish citizen set off a bomb independently on Britain then it is terrorism. If a Scottish solider under the orders of the Scottish government sets off a bomb in Britain then that is an act of war. So you can fight terrorism with war because not all terrorism is an act of war.

War itself, including revolt, is not terrorism. By definition, war is an armed conflict between two or more states or non-state actors in effort to carry out certain goals. The American Revolution was a perfect example of a revolt, not terrorism. However, even in war, there are certain amount of limits that prohibits belligerent parties from inflicting unnecessary suffering, such as deliberately shooting civilians, abusing prisoners of war, using chemical and biological weapons in combat against enemy combatants, and attacking neutral service members not posing a lethal threat and not involved in the war. Most of our soldiers during the American Revolution generally followed the rules of regarding the treatment of British and Hessian prisoners of war.

Terrorism is a form of tactic by delivering explosives or other objects with the purpose of committing bodily harm or death upon non-combatants and/or non-combatant property through fear and intimidation to obtain political or religious goals. Terrorists did not go after the people who are fighting them, but instead against those who are not involved in fighting, simply because of their disagreement with their political or religious opinions. For example, 9/11 is terrorism because Al-Qaeda hijacked commercial planes filled with civilians and use them to deliberately attack the World Trade Center and the Pentagon on September 11, 2001, just to express their disapproval with our policy in the Middle East and just because we are non-believers to their twisted radical beliefs. Also, terrorists do not follow the same rules during our war on terror, and often target non-combatants to put fear into the populace and destabilize their existing governments. They are usually a rebel force and are usually small in size.

If war is a form of terrorism than you concede that our founding fathers who won independence against the British in the American revolutionary war were terrorists.

No fighting for a cause on behalf of others is not terrorism. Terrorism is using violence and fear force a specific ideology on someone. As in "Admit there is no god but Allah and Mohammad is his messenger or die".

See the difference?