As far as I can tell, Ukraine mobilized less than 500 thousand people for the war effort. But given that the war is an existential crisis for the nation, why didn’t they mobilize a few million men in an effort similar to World War 2?
Unless they tell us...
But at a guess there are a number of reasons.
(debunking) if they'd sacrificed 2-3 million people...
Well, yes, but maybe if they took that kind of approach, to their own people, support for the war would collapse?
Wagner's Bakhmut's convicts did not have a choice and they were convicts, serving long terms for violent crimes. Not going to be winning the sympathy votes, are they?
Wars need sacrifice to win, but throwing away lives risks collapsing the will of the soldiers and the larger population. This is what nearly happened to the French (in 1917) and did happen to the Germans (in 1918).
(debunking) But Russia mobilized 20+% of men in WW2...
From Hitler's announcements in Mein Kampf about lebensraum and race it is clear that the Nazis consider the Slavs untermenschen, good to be killed at will for the good of the master race. For Russia, and Ukraine, in WW2 surrender, to the Nazis, is not an option, as the Nazis will at best starve you once you do. There is a whole plan of colonizing Ukraine's rich farming land - Germany is land-poor - by starving the locals out of existence. So extreme mobilization can be sustained: they don't have a choice.
Not to mention those happy little NKVDs and Gulags, for those who failed to see the light.
And... would the West continue supporting Ukraine if its government publicly put it in place things like summary executions for deserters and draft-dodgers, to achieve Russia's WW2 degree of coercion? My thinking is no: sympathy for the country would dwindle very quickly. So there is also a very real risk there too.
500k is quite a lot out of 40M
Especially with different age demographics than in WW2.
This war may also last years. If you mobilize everyone at the same time, it might be very difficult to sustain that, economically, for that duration.
Ukraine's recruitment process says 2 things:
- you have to report for assessment
The subpoena does not guarantee that men will be sent to the army...According to him (Roman Horbach, head of the personnel department of the command headquarters of the Ground Forces), in most cases today, citizens are called to the territorial recruitment centers in order to clarify their military registration data.
- you may very well not be sent to the front, as they need specialists, not just warm bodies.
Horbach noted that they are currently mobilizing those who can work with new types of weapons that are being transferred to Ukraine by Western partners.
"Today we need specialists both for new types of weapons provided by partners and to replenish losses. First of all, we are mobilizing personnel in certain accounting and military specialties", - Gorbach insists.
From 1. you see that they are not closing the door on upping the numbers, later. And 2. gives you an idea why they are prioritizing.
They also have issues with training bottlenecks and equipment, arguing for a longer, less concentrated-in-time effort:
In December Ukraine’s top soldier, Valery Zaluzhny, told The Economist there was no immediate need for massive mobilisation; his main problems were armour and munitions. Sources within the general staff insist that is still the case. Moreover, there are natural limits to the numbers of soldiers Ukraine can absorb, says Viktor Kevlyuk, a reserve colonel. “You can’t mobilise 6,000 if your training ranges can hold only 3,000,” he says.
We'll see the numbers once this mess is over. Sadly, looks like both will be at it for a while. WW1 UK enlistment (never draft, though it was very coercive as time went on), gradually took down all sorts of limits on who could serve: minimum height requirements went down year by year. This, Ukraine, is only 18months in.
Modern equipment is just mostly harder to use effectively than WW2, let alone WW1, gear so throwing bodies at the problem just doesn't work as well as before.
Last, warfare is changing in nature
The Economist reports that the front line is just very much more sparsely manned than it was during WW2. Packing anymore men together in an age of drones, satellites and precision long range ammo just gets more of them killed, without significant military advantage.
This jeopardy is reflected in a curiously sparse battlefield. In Ukraine some 350,000 Russian troops are arrayed on a front line stretching 1,200km (750 miles)—around 300 men per km and, at times last year, less than half that. That is around a tenth of the average for the same area in the second world war, notes Christopher Lawrence, head of the Dupuy Institute, which collects such data. Battalions of several hundred men fill areas that would once have been covered by brigades of a few thousand.
(incidentally, though that is not relevant to the question here, that article posits that this incapacity to mass troops may be one factor in limiting offensive action: the by-the-book 3x local numerical advantages needed by attacking forces remains out of reach)
They may also be hitting the limits, short term at least, of what their population is willing to do.
Another difference is over who is being called up. In the first wave most of the recruits were voluntary; queues outside draft offices were a frequent sight. Now officials are recruiting from a much less enthusiastic crowd.
Which dovetails with my first point: if the Ukrainian government gains a reputation for being willfully wasteful with their soldiers' lives, as this question seems to suggest ought to win the war, then support will be at risk. By the soldiers, by the draftees, by the larger population. Giving into Russia will seem a better choice.
To fight a war, you also need money and equipment, not just soldiers. The Ukrainian GDP is the worst in Europe; the country is by all means in bankruptcy. That it had not collapsed is only because the west (US, UK and the EU) is financing it. Most likely they would go immediately bankrupt if they were mobilising significantly more people, not to mention that they would not be able to equip them. If it goes bankrupt, e.g. if it cannot pay pensions or health care any more, the population would quickly turn against the leaders.
Modern warfare isn't quite like WW1/WW2 warfare. We have better weapons and better techniques.
The elite troops of WW1/WW2 that tore apart the war-long defensive lines use simplified "primitive" versions of modern standard infantry tactics, things like covering fire and leap frogging and combined arms being bread-and-butter today.
In comparison, most WW1/WW2 armies where thrown en-mass into meat grinders in basically frontal assaults. It was amazingly inefficient in terms of human lives.
A smaller, better trained force can both have fewer casualties and be more effective at claiming territory. And that is what Ukraine is doing.
Moscow has 3-4x the number of people reaching age 18 that Ukraine has per year. If Ukraine attempts to win this war via mass attrition, losing 1 soldier for every soldier Moscow throws into the blender, they will bleed out rapidly and collapse.
Ukraine has to maintain a large kill ratio to stay in the war (let alone win), or win the war rapidly before Moscow can match their conscription rate.
And, as best we can tell, Ukraine has been doing this. Since the start of open hostilities in the Moscow-Ukraine war in 2013, Ukraine has transformed their army using western/NATO style training and tactics, together with some amazing home-grown "regional defence" systems.
They spent nearly a decade producing veterans trained in modern infantry warfare and defence, and provided local autonomy to defend each region if it was attacked. And it worked in the initial invasion -- Moscow took insanely lopsided casualties as its ability to project force very far from a railhead caused their supply lines to collapse under relatively light pressure.
Ukraine is attempting to maintain the same high level of professionalism and training in its military while bulking its army up. This means maintaining a 5:1 kill ratio in battles against Moscow's invasion forces, plus training up large numbers of specialists (drones, tanks, APCs, artillery, mechanics, technicians) for the flood of Moscow and NATO-provided weaponry.
Mass conscription -- another million poorly trained cannon fodder -- would be marginally useful, but mostly result in a million dead Ukrainians for a few km of territory, and it would deplete the pool of people that can be trained to be modern professional troops, and would cause a massive dent in the Ukrainian economy.
At this point, Ukraine appears to be successfully bleeding Moscow out. It is better armed than it was at the start of the war, Moscow is worse armed, and its people are more motivated to fight than prior to the war. Its supply of weaponry continues to improve in quantity and quality, its troop numbers are staying steady or increasing, and it is pushing Moscows lines back at multiple locations simultaneously while holding onto a large mobile reserve to drop like a hammer if any of the invaders lines crack.
Currently there are roughly 1 million people under arms in the Ukraine, but that includes regional defence forces and civil police not on the front lines. Full mobilization would bring this up to about 7 million. Maintaining the current forces requires 20% of Ukraine's GDP, which doesn't include external supplies of arms. If you wanted to expand the 500,000-odd primary force to 5 million at current quality rates, you'd need to spend more than 100% of Ukraine's GDP on it and increase external supplies 10 fold.
Ukraine appears to be training and supplying high-quality troops at the highest rate it can sustain. An attempt to increase numbers beyond what it has would require that it cut corners and send troops with significantly worse training into the bloodbath.
Because they couldn't properly arm any more.
Arguably, if Ukraine got a better support in terms of military equipment and ammo, it would have a chance to mobilize more soldiers, train and arm them properly, and then regain their land back in a quick offensive. This wouldn't necessary mean more total losses, as the war would be over sooner.
Especially getting large quantities of fighter jets (to achieve air dominance) and long-range artillery/missile systems early on in the conflict would have turned the situation to Ukraine's favour, most probably without additional causalities. It would saved enough civilian lives to compensate for lives lost in combat, even if that would mean to mobilize significantly more soldiers.