Ukraine eventually has to decide what kind of long-term defense policy it will adopt. There are basically two choices, the nation-in-arms or the current system that has a relatively large regular military plus the territorial units, which have become legendary for their effectiveness against the Russian invaders. Ukrainians admire those who fight as organized militia against a foreign threat. The territorial units, all formed after 2014 who fought so effectively against the 2022 invasion, might be able to survive as effective local forces that receive training, weapons, uniforms and recognition from the government as well as pay for the time they are on active duty for training or long-term conflicts.
This is a version of what Israel employs to become what is recognized as has the most powerful armed force in the Middle East. Israel manages to achieve this with a population of only eight million. One reason for this is the Israeli use of reserve troops who are recruited from the regions they live in and the brigade names originally came from those regions. While only two percent of the Israeli population is in the active army, nearly five percent are in the reserves. There are former full-time soldiers who train regularly and can be called back to active service quickly. This is called the "reserve system" and it is a relatively recent development.
It all began some two hundred years ago, when several major European nations began conscripting civilians for the military on a regular basis. These soldiers served for only two or three years before being released. Shortly thereafter, several nations came up with the notion of bringing some of these former soldiers back to the army in times of national danger. This was done by enrolling discharged soldiers in reserve units and often having them show up in uniform and with weapons for some training a few times a year. Thus began the "reserve system," which enabled enormous armies to be created quickly and relatively inexpensively. World Wars I and II would not have been possible without the reserve system.
Some nations, like Israel, Sweden, Finland and Switzerland, took the reserve system to an extreme. These four nations conscript a large portion of the adult males into the reserves. As a result, full mobilization calls up so much of the population that it severely disrupts the economy. Sweden and Switzerland are neutral and depend more on the threat of mobilization. Finland uses its mobilization force and its reputation of defeating past Russian invasions.
Israel has had to mobilize several times in the past and will probably have to do it again. Israel has to win quickly and her enemies know that. However, Israel has adapted its economy to full mobilization. Forty years ago, such a mobilization put 15 percent of the population in uniform but now it's less than half that. That means Israel can keep fighting for a bit longer while fully mobilized. This has proved to be a powerful deterrent.
Israel, Sweden, Finland and Switzerland all depend on units formed around reservists from the same area. While some reservists are used to reinforce active-duty units, most mobilize and go to war with their local reserve units. In effect, reservists serve in units that will, quite literally, defend the homes and families of the reservists. That is a tremendous motivator to learn military skills and perform your duties effectively. Britain continues to use this system for its army reserve and West Germany adopted it during the Cold War while South Korea still has a similar system. In the U.S. most of the reserve troops serve in National Guard units belonging to individual states in peacetime and are mobilized into the active army for foreign wars. The National Guard evolved from the colonial militias that existed before the revolution that turned the colonies into the United States.
Israel is unique in that its reservists, especially those in combat units, are frequently mobilized in peacetime. About 30 percent of Israeli reservists are mobilized each year (for more than a few days), often for only a week or two. About two-thirds of those mobilized are combat troops. Not surprisingly, half of reserve troops are married and 40 percent of them are women who are also conscripted. Reservists serve until they are 40 and physically able, and can continue until 51. Most women serve in support jobs, which are numerous enough to use all the female reservists.
Switzerland still has a nation-in-arms system with all members of the reserve army keeping pistols and assault rifles at home. This allows Switzerland to mobilize a large force in a few hours, all of them armed and knowing their local defense positions and what their duties are.
Sweden is reviving a version of the Israeli system they had during the Cold War. In the 1990s Sweden eliminated conscription, which is essential to make these systems work. Now conscription is back, along with plans to join NATO.
Many Ukrainians still want to join NATO but that cannot be done (or has not been done) while the nation is at war. Ukraine has the full support of NATO, at least in terms of weapons and military supplies in the fight against the Russian invaders. Forcing the Russians out of Crimea and Donbas will be costly in terms of casualties but if the Ukrainians demonstrate a willingness to do it the Russians may decide to cut their losses and leave. After that the Russian threat will remain, as it has for centuries.
Ukraine may opt for the Israeli system long-term because the Russian threat is not likely to go away and depending on NATO Article 5, which requires all NATO nations to come to the aid of any member attacked may not be sufficient to keep the Russians out. Israel has never considered joining NATO and instead maintains strong economic ties with NATO countries, including the arms trade. Ukraine does want to join the EU (European Union) which is all about economic cooperation without depending on NATO for military reinforcements. Israel also has nuclear weapons and the means to deliver them by ballistic missiles or from submerged submarines using cruise missiles.