What could increased tension on the Korean peninsula lead to?

S Korea spends big on defence because of a hostile neighbour.
Failure to shoot down North Korean drones in its airspace on Monday has caused alarm.
The military has apologised and President Yoon Suk Yeol says the incident shows a lack of readiness.
Pyongyang has tested at least 90 missiles this year.

How serious could increased militarisation be for the region?