A counterexample: Costa Rica (where I'm from). We haven't had an army for the last 70 years and still remain a country. Superpowers (e.g., US, China, Russia) might need armies as means of mutual deterrence. Smaller countries not so much.
"Countries Without Militaries" by Kathy Gilsinan (Nov 11, 2014) at https://www.theatlantic.com/international/archive/2014/11/co... specifically discusses the case of Costa Rica: "After 7,000 U.S. servicemembers deployed to the country in 2010 to assist in counter-narcotics efforts, Bolivian President Evo Morales said Costa Rica did have an army: the United States military." Indeed, that articles notes a lot of the complexities when you dive in. The vast majority of countries have obvious militaries, and of the rest, "Virtually all the countries the CIA lists as having no formal militaries have some form of security service, and the degree to which they focus exclusively on internal threats varies". If there's absolutely no threat then you don't need a military, but for the vast majority of countries, that is not reality.
> So, Who Protects Costa Rica? Costa Rica maintains its military-free status and does not command any military units or house any war weapons. However, the country does maintain alliances with other countries, such as the United States, that can be expected assist in the event of war within Costa Rica. https://qcostarica.com/costa-ricas-military-abolition-histor...
Edit: It directly contradicts the usage of the claim that small countries do not need a military. Essentially borrowing deterrence from another doesn't result in the world being military free.
it's probably a good thing that not every country in the world needs to maintain a full-scale military, but this only works if you have a powerful ally whom you can trust to defend you. the fact that costa rica is able to exist without a military doesn't imply that the US could also disband their military.
Then you can say how wonderful it is to save a fraction of a percentage point of your GDP on defence and how it worked so well until the day it was needed.
At the end of the day, it isn't the presence of a military that makes the difference, but the strength and spread of the country's treaties with other nations.
Ukraine example shows that treaties are worthless. Neither USA nor UK did anything to protect its territorial integrity as they agreed upon.
https://en.wikipedia.org/wiki/Budapest_Memorandum_on_Securit...