No. Pacifism doesn’t work as can be witnessed throughout the world. In fact, as I write this, Nicaragua is in the middle of a government crisis/meltdown where government soldiers are attacking and killing civilians.
The best reasons, I believe, that Costa Rica has been left alone is the following:
a) Huge investment by the USA for regional peace due to the proximity of the Panama Canal. The Panama Canal is still a vital access route for many countries of the world.
b) Related to ‘a)’ is that China is investing heavily in Costa Rica. China is in a global long-play resource solution. They are securing food (fruits in Costa Rica, largest pork producing company in the USA, heavy investments in natural resources in Africa).
Related to a) & b): There was an actual bidding war between the USA and China when the Panama Canal was expanded several years ago. They both wanted to spend billions of dollars to make sure the canal was built properly to ensure global trade continued as smoothly as possible.
Therefore, the two largest superpowers in terms of economics and military, have a huge financial interest in regional peace.
c) Costa Rica has been blessed with some great leaders with international influence and progressive domestic policy. For a country that just recently celebrated its 5 millionth citizen, they have a lot of influence in the international stage. Oscar Arias was President during the 1980s invasion by US troops into Nicaragua and Panama. He was also President again about a decade ago when Costa Rica had a seat on the UN Security Council (the irony of a country sitting on the UN Security Council but not having their own military).
Currently students throughout the country are taught English in elementary school, and all future generations will have exposure to English as they continue to move into a service economy, and away from a product economy (coffee, pineapples, etc).
d) Who would invade Costa Rica? Panama, to the south no longer has a military. Nicaragua to the north, would love to invade, and tried to steal some land as recently as five years ago (resolved at the UN), but it would be a losing proposition. Nicaragua would get no international support and Costa Rica would get the support of the USA and/or China.
Therefore, the immediate neighbors don’t have an army or a strong enough of army to fight back the USA.
This would leave other countries would attack. They’d have to attack via the sea – slow, and would have to have a Navy, which would be picked up by radar days, if not weeks, in advance. Or a country would have to go through another bordering country. Again, slow and highly unlikely.
Keep in mind that the United States Coast Guard has patrol boats off the coasts of Costa Rica constantly on the lookout for drug runners. Additionally, the US Navy has tracking of all large ships in the world, so any major change would be immediately noticed by the US Navy.
Assuming a country made it to Costa Rica, and attacked….what is their prize? Amazing wildlife. Some unearthed gold. There are some oil reserves off the Caribbean Coast that the Chinese are rumored to have purchased the drilling rights to (unsubstantiated), but outside of that, there isn’t much here worth spending the billions of dollars it would take to conquer.
What makes Costa Rica amazing is the natural beauty and the amazing people. Conquerers prefer oil and natural resources.
