<< War happens when one country declares war on another.
The Gulf War was not really a war. Neither was Vietnam, Somalia, Grenada, Korea or Panama.
Repeat after me: PO LEE SSS ACK SHUN >>
Technically, "war" is a formal declaration of hostilities by one government against another.  In the real world,  struggle is a simple fact of existence between any two given countries, and runs along a continuum which looks something like this:
alliance/active cooperative partners --->  peaceful coexistence ---> non-violent competition ---> Military Operations other than war (MOOTW) ---> small scale contigiencies ---> low intensity conflict ---> high intensity conflict ---> major theater wars ---> wars of mass destruction.
Generally, a status of MOOTW or less is considered "peace,"  small scale contingiencies and LIC to be "police actions" or whatever the politically expedient term is,  and HIC or above to be general conventional war.  War of mass destruction is a special category, of course.  
To put these in perspective,  U.S. operations in the recent past can essentially be summed up like this:
Grenada:  small scale contigiency
Panama:   low intensity conflict
Gulf War, Vietnam:  high intensity conflict
Korea:  borderline major theater war
WWII:  multiple major theater war