I think the key to understanding the Klingons in TNG and DS9 is understanding that without a definitive external enemy the Klingon Empire starts devouring itself - the Klingons devolve into internal strife and petty piracy. Remember that while Star Trek canon can be fairly squishy (not even counting whatever bullshit nu-Trek is doing), peace between the Federation and the Klingons was imposed by god-like aliens (how long that mandatory peace lasted is up for debate). You could make the argument that the Klingon Empire, which was presented as a fairly unified structure in TOS, started to fall apart when they could no longer fight the Federation.
I think the key to understanding the Klingons in TNG and DS9 is understanding that without a definitive external enemy the Klingon Empire starts devouring itself - the Klingons devolve into internal strife and petty piracy. Remember that while Star Trek canon can be fairly squishy (not even counting whatever bullshit nu-Trek is doing), peace between the Federation and the Klingons was imposed by god-like aliens (how long that mandatory peace lasted is up for debate). You could make the argument that the Klingon Empire, which was presented as a fairly unified structure in TOS, started to fall apart when they could no longer fight the Federation.