Don't forget the Mexican/American war, the Spanish/American war, the unending "Indian Wars", and various other military expeditions during that period.
It's probable that the War of 1812 showed America how unprepared it was for conflict with a serious power.
The civil war from 1861 to 1865 required the complete commitment of both sides, with the Union in particular developing massive industrial capacity to help the cause.
This rapid and urgent industrialization was further developed during the Reconstruction phase when a large chunk of the country had to be built back up from ruin.
If these two conflicts never happened there wouldn't have been the same urgency to develop industry. It would be much more of an agricultural economy like the southern states and not like Ohio, New York or Pennsylvania with their enormous appetite for large-scale manufacturing.
If that was the case the US would be utterly unprepared for any conflict in Europe. As it was the US military was in really rough shape prior to the outbreak of war in Europe. There was no pressing need for a large, well-equipped standing military since Mexic
The point was we were never on a wartime economic footing in the same way were were in WW II.