The economy at full employment means that all people are employed, except those who do not wish to or cases of transitory unemployment. This is a number of approximately 5% of people without jobs.
Rarely does an economy reach full employment. If everyone is employed, there is a lot of money in circulation and the economy is warm.
In this way, if the Government goes to war, it will have spent more and still, if funding is granted, there will be more money in circulation in the hands of the public. This can boost an inflationary process, since inflation is a monetary phenomenon, associated with the amount of money in circulation.
