The The Pirate Crusade never really ended at Hardbottle. Though the above ground parts of the island were quickly conquered, the halflings retreated into their extensive tunnels and burrows where they proved impossible to dislodge. In addition the rocky, mountainous island was a perfect have for guerilla fighters.
While House O'Brian has controlled the island on and off for last 75 years, and occasionally installed puppet governments they never really subdued the halflings entirely or broke their spirit. They never dared venture down into the burrows except in great numbers and with violent consequences.
It’s fair to say that the main accomplishment House O'Brian can lay claim to with their attempted conquest was to breed some of the most experienced, ruthless, and brutal guerilla fighters in all of the The Thousand Isles. The Kneebiters.
Masters of stealth, concealment and hit and run tactics, the halflings typically operate in small groups, semi independently but with coordinated goals and strategy.