You have voiced a very subtle topic.
The point is that the GDP of a country that is actively at war may look good on the one hand, but on the other hand you have to realize that during a war the GDP generates products and services that do not create additional value for the economy. Take for example the terrorist country Russia - they claim that the economy is doing well, but in reality the economy is collapsing and the population is poor. Why ? Because about 40% of russia's budget goes to support the terrorist war - ammunition, shells, equipment, ammunition, payments to terrorists of the rf army...... And all this, after a very short time, turns into smoke, burned debris, corpses of their soldiers (and the loss of able-bodied population).  So the GDP of a country at war is not equal to the same GDP in peacetime !