I'm slowly reading a book on Henry V of England.
In the usual explanation of how Medieval warfare is a wholly different thing than modern warfare is a nice collection of details on the office of herald, the way loot is divided*, the importance of ransoms, etc. there was a bit about what are best called early adventuring compacts:
"Another more sophisticated method of distributing the dangers and rewards of war were the contracts between soldiers which made them "brothers-at-arms." Such agreements were genuine legal bonds, sometimes for life, sometimes for a specific period, which were usually arrived at by a solemn oath or by sealed letters. Their terms normally provided that the brothers-at-arms should share equally in all gains of war, and should contribute equally to ransoms if one of them became a captive. If both were taken prisoner, one served as a hostage and the other went to raise the ransom for both. All classes of soldiers might become brothers-at-arms -[. . . ]"
- Margaret Wade Labarge, Henry V, p. 67
It goes on to give the example of an English duke and a French duke who were brothers-at-arms despite serving different kings and having different allegiances. Still another specified two captains would pool their loot and send it to London - whoever got home first would invest it, and if only one got home he would get all of it except 1/6 set aside for the widow of the other.
So, early adventuring contracts. Maybe pooling all the loot, dividing it up, and providing for healing and resurrection of the slain (basically, paying a ransom to death!**) is not a strange modern let's-all-get-along thing but rather an extension of how loot-hunting men-at-arms dealt with similar issues.
* For example, as of the time of Henry V and soldiers serving for pay and loot not out on a temporary callout, the finder gets 1/3, his captain 1/3, and the king 1/3. The captain also pays 1/3 of his take (so, 1/3 of that 1/3) to the king.
** Which is an outstanding gaming concept, right there. It would explain and/or justify level based costing for Raise Dead in D&D games.