One of the main challenges of maintaining peaceful international relations is the escalation of distrust and the ensuing arms race.
The possibility that others might attack you is a reason to arm yourself. But this step will in turn be interpreted as a threat by the other, who will in turn arm itself (even more). Etc.
Aren’t there ways to simply invest in purely defensive weapons? So that your efforts to remain safe do not in turn threaten others? Which in turn allows others to also de-escalate?
In other words, are there military set-ups that are useless for offensive actions but good enough for defending a country?
Technically SAM systems are purely for defence but to get a complete set to defend you need a lot more than just anti-air.
Defence deterrent is based a lot on potential counter attack so if you don’t have a counter attack potential it’s kinda safe to attack you. Nuclear bombs are an example of this, they are the most aggressive and destructive which makes them very effective for deterrence.
One thing Ukraine has shown is that fortifications are super important which are purely defensive. But to guard a long defensive line without a massive standing army you need a crapton of drones which can be use both offensive and defensive.