In historical international usage, largely superseded by modern law, the shedding of blood, or at least the use of force to achieve an end, such as the conquest of a territory, or the successful defense of a territory, was often seen to confirm ownership in a case where it might otherwise be doubtful. Or that the result of combat (and bloodshed on both sides) was seen to confirm the provisions of a treaty.
For example, Spain had originally owned what became the Louisiana Purchase, but it was under French administration by virtue of some shady dealings when Napoleon sold it to the United States. Spain later contested the sale, claiming that, among other objections, that Napoleon had no right to sell it. But the fact that the United States had successfully defended New Orleans against the British in the War of 1812 was considered to be strong ground for disregarding the Spanish claims. There were other reasons, too, including the fact that the USA had asked Spain about buying it, but Spain had directed the USA to talk to France about it instead.
Some of what I've said about Louisiana I've unfortunately been so far unable to confirm (having heard it said by someone who I thought was an authority on the subject), but there is an interesting discussion about it on Wikipedia.