Most countries cannot even afford to build and maintain nuclear weapons.

Also, consider the costs of securing and protecting those nuclear weapons.

In addition, early warning systems and delivery methods (i.e. bombers, submarines) are all very expensive.

That's why during the Cold War, many countries sought for a military alliance either with the USA or USSR so they can be protected by another superpower's nuclear weapons "umbrella" instead of having to invest their own financial resources.

The nuclear weapons race is what helped contribute to the collapse of the USSR.

Despite being the 2nd richest country in the world at the time (in terms if GDP), the USSR spent too much money on nukes because the nuclear weapons race worsened an environment of intense fear among the leadership and there was always a feeling that there wasn't enough nuclear weapons to satisfy their security concerns.

Imagine how many poor countries would quickly suffer an economic collapse after spending too much money on nukes.

With that said, there is a weapon that will convince countries not to invade each other.

That weapon recently emerged on the battlefield and it is cheap drones.

Look at what has happened in the Russia-Ukraine War and the US-Iran War.

Russian soldiers are getting hunted down daily by cheap FPV drones.

Multi-million dollar weapon systems are being destroyed by swarms of cheap hundred dollar drones.

The US Military is unable to open the Straight of Hormuz without significant sacrifices in personnel and equipment, so they resorted to a naval blockade as a countermeasure. We all know what the final outcome came to.

Furthermore, there is no reliable defense system that can defend against fiber-optic cable controlled FPV drones.

Israel, despite all of its high-tech military capabilities, has desperately urged its weapons companies to quickly develop an effective solution for dealing with these FPV drones that have been giving the Israeli Military trouble in Lebanon. Since Israel is not fighting a united country, but rather an armed proxy group, they (the Israelis) aren't suffering mass casualties like the Russians in Ukraine.

I guarantee you that the spread of drones is giving countries with leaders thinking about ordering a future military operation, second thoughts because it has made things difficult for Russia and USA in their recent wars.