well, imagine yesterday you had a river border with retarded guyana, abosolutelly peacefull country, and now that border is suddenly with venezuella who just ate half of guyana and insanely patriotic
in situations like this venezuella can just do retarded shit like cross into brazil territory, maybe take over some island on the river that was brazilian, but venezuella will claim that its actually venezuellan icland on the river and they don't care if guyana before admited it to be brazilian land.
green part is forest, you can cut it down for timber
plus if Brazil will do nothing, they will look weak. maybe Lula is ok with that, but different retards in brazil could exploit it, and in any way brazilian weakness could invite American-UK-French strength. Like what if Americans intervene and start fighting with Venezuella and you as Brazil was sucking dick at the begining of this dispute, in the middle when hot war started you realize that "Holy fuck this was is generating legit refugee crisis, with forest fires from bombs, illegal trade of weapons, brazilian people go to there as mercenaries and return radicalized and begin to form militias that challenge our central power..."
i dunno, i'm drunk and iwant tosleep