Say you're a knight or baron or just generally a landowner who swears fealty to a much more higher title than you. One day a war breaks out between a rival realm or raiders from a more tribal-like one attack and your lands get devastated, how did you recover? Especially if almost all your peasants/villeins and serfs were killed in the attack.
Theoretically, his lord should help
Feudalism lasted a long time in many countries with different cultures, religions, natural conditions etc ... Therefore, any generalized and generic answer would be certainly lacking . That being said, let's give it a shot.
Basic relation between a lord and a vassal was granting a fief in return for a service. Vassal would swore fealty to the lord, promise to come to his aid in case of war (with or without number of men, depending on size of fief) , pay some taxes (usually) to the lord, sometimes to uphold laws of the realm and to protect state religion (church) etc ... Although fief was usually hereditary (especially in Europe) vassal was not strict owner of it. In fact, there is a number of cases where king would take away possessions of a treacherous noble and give it to another (for example James II took away lands of powerful Douglases ) .
In any case, fief was main source of income for a vassal, and means to fulfill his obligations towards a lord. Larger and richer the fief, larger were those obligations. Ruined and burned fief, with serfs slaughtered was not worth much. It would be akin to expecting same job commitment from an employee who's salary was severely reduced. Theoretically, it was obligation of the lord to help his vassal in time of need. One measure would be to move some serfs from lord's own lands to vassal's . Depending on the phase of feudalism, this could be done with or without serf's consent. Usually, they did try to give some incentive to serfs like larger piece of land, bigger share of the crop etc ... Of course, in some cases lord's lands would be also in dire straits. Lord could reduce obligations for his vassal (come with two men instead of ten, and bring 10 gold pieces instead of 100 ) . Of course, there were the cases with obstinate lords who didn't want to reduce obligations from their vassals, which led to vassal's revolt or working to death remaining serfs (and having them revolt) etc ...
In the end, it is worth mentioning that feudal political theory emphasized Noblesse oblige, or in other words that privileges that lord has over his vassals and surfs also entail his duty to help them and protect them in time of need. Of course, in reality that could be much different, but at least theoretically it would be the duty of greater noble to help those bellow him.
I am basically doing this from memory based on what I’ve learned over many years, so something I may be mistaken about, or misstate some things, or I could be confused and be dead wrong.
So I welcome anybody who spots the areas that I’m wrong or off and corrects them. I’m not sensitive in that I do not know everything and I am welcome any corrections to what I will be saying below.
Medieval warfare was a long process of making war. There are at least three factors that we take for granted today that they did not have:
The first is communications. They had to send runners over land and in some cases overseas to find or communicate with allies or family members who married other nobles from other countries.
Depending how bad you were just devastated, the second factor is raising an army, and knowing how to train new members and even organize them on a battlefield. Back then it was done with flags and horned instruments, each with their own meaning.
And thirdly, since you had mentioned that most all your peasants were killed in the attack, you will need to recruit others to fight for you. Unless you’re rich, or since the people who used to work the land had ownership like crop sharing (if you allowed ownership), you can use incentives such as fighting for you you give them a free house plus a stipend to help them get settled in your lands. Recruiting can take a very long.
And more than likely your crops were destroyed during the attack and you’re gonna need people to work your land so that you can make money And feed your people from the crops you grow. So whoever you recruit will not only work the land, they will also be obligated to fight for you.
Now if you’re a Knight or a Baron, these two ranks are on the low end of being royalty. In fact, the King or Queen can bestow Knighthood to anyone for any reason, and that does not entitle them to royalty benefits.
And most people earn the title of Knight by fighting for their Baron or Prince, and other royalty above them. You have to train in the fighting arts for many years, usually apprentice under another Knight, and be recognize for bravery in battle to become a Knight. So as a Knight you really are an elite fighter for whomever you work for.
Now a Baron is a landowner who owns one or more estates, and maybe has a castle, and lots of peasants working all his lands. When a Duke or Prince or other royalty above a Baron request that he joins in on a fight, he will enlist many of his peasants to fight for him, otherwise he will kick them and their families off his land.
If you were a Baron who were attacked and lost most of your peasants, and since you are part of the royal family, you will have a easier time recruiting people to both work your land and fight for you if called upon. Hopefully you have some Knights available to train your peasant Army.
One other thing that I recall is that Knights had to provide their own weapons and armor. That means they paid for it out of their own pocket. None of the members in the royal family gave them anything. Same thing with the peasants who you want to fight for you as a Baron.
Unless you are super rich and can provide the weapons and armor, you would require your peasants to provide at least a shoe ld, a sword, and some kind of rudimentary armor to protect their heads and body. But it will not be on the level of what a Knight wears or arms themselves.
Again, I made this post basically from memory of what I learned about Medieval war and who provides a lot and how peasant recruitment is done.
There are many other factors, and generally if you have a large family who are on the same level of you or higher, you can expect help from them in recruiting and training and possibly even providing you with soldiers. Here would make a difference because if you’re fighting along side your family member, part of their army can become part of yours and both will fight together as a unit.
So if I made any mistakes or mis-stated anything, please Feel correct what I said. But I think I got the basic principles right, for to answer this question completely, there have been volumes of books written about the subject.
I hope this helps.