Adopting the Quantity idea group usually solves any manpower deficits. Their first two ideas should be enough: If you prefer to use other idea groups, you still have other ways to address your needs. This mainly involves increasing your national manpower. You can do that by:
Developing your provinces’ base manpower Building barracks and training fields in provinces with high manpower Building soldier’s households in grain, livestock, or wine provinces
You can also get an immediate supply of manpower from:
Slackening recruitment in the Military tab Exploiting provincial base manpower
Alternatively, you can make adjustments to your manpower loss by fighting smarter. Consider these aspects to conserve your manpower:
Hire mercenaries Keep attrition low Optimize sieges
National Manpower
Base Manpower
Your national manpower is the sum of all of your provinces’ local manpower. Each point of base manpower in a province adds around 250 to its local manpower. Developing a province’s base manpower costs Military mana. This cost is relative to that province’s total development. One strategy is to exploit a province’s base tax. This lowers that province’s tax dev, which also decreases the mana cost for improving its manpower.
Barracks and Training Fields
There are two military buildings that modify local manpower. These aren’t cumulative modifiers. Building a training field will replace the barracks in the target province. Since these buildings give percentage bonuses, they’re more effective in provinces that already have a high base manpower.
Soldier’s Households
Soldier’s Households increases a province’s manpower by 750. You get double that if you build it on grain, livestock, or wine provinces. This is a manufactory that becomes available at Admin Tech 15. You’re normally limited to one manufactory per province. However, you can increase that limit by clicking on the “Expand Infrastructure” button in the Building UI. This requires the province to have at least 15 total development.
Emergency Manpower
Slacken Recruiting Standards
The “Slacken Recruiting Standards” button in the Military tab will instantly provide you 2 years’ worth of manpower. This costs 5% professionalism. You gain professionalism by drilling your armies, but this method only yields 1% professionalism per year at most. The other way is by recruiting generals, which costs 50 Military mana. Each recruitment gives you an immediate 1% professionalism. This means that 2 years of manpower is worth 250 Military mana. Note: Be careful not to abuse this. You may fall behind in Military Tech if you spend too much Military mana.
Exploit Manpower
Exploiting a province’s base manpower will give you 5 years’ worth of its local manpower. This reduces its base manpower by 1, and can only be done every 20 years. This short-term gain can be useful if you have a mission that requires you to have a certain amount of manpower.
Conserving Manpower
Use Mercenaries
Mercenaries may cost a lot, but they’re usually worth it. This is because they come with their own manpower pool. This makes them useful for conserving your own reserves both in peace and in war. Note: Hiring mercenaries will reduce your army professionalism by -5%.
Avoid Attrition
If an army’s supply weight exceeds the supply limit of a province, that army will take attrition damage. Attrition can get more severe depending on:
The number of regiments in an army The terrain and climate
Large armies can get decimated just by standing on arctic mountains. For example, a 20k army suffering from 5% attrition will bleed 1000 manpower per month. To avoid this, you should: If you think one of your divisions will encounter an enemy, have the rest of your troops re-converge on them. A small division can get wiped out immediately, resulting in more manpower loss.
Optimize Sieges
An army that’s besieging a fort will always take at least 1% attrition. Each fort level has a corresponding number of regiments needed to maintain a siege. You can check this in the siege panel. You should only have the minimum number of regiments plus an additional one on this task. The extra regiment will soak up the attrition damage while the siege progresses. Ideally, you’ll want to have artillery in this army. Artillery gives a bonus when sieging forts. You can also order an artillery barrage to make a breach in the fort’s walls. Use these advantages to quickly end a siege, so your troops won’t keep dying from attrition.