The Belfast agreement happened because the IRA was a spent force and it finally dawned on them that they could not achieve their aims by force.
The real credit for peace in N. I. lies with the security forces, they rolled the IRA up like a tube of toothpaste.
Blair claimed credit along with Clinton and the EU for the IRA giving up violence, the truth was McGuiness and co. were desperately looking for away out when along came Blair and saved their skins.
If the IRA have given up Violence why has Bombings/Shootings in Northern Ireland increased in the last few months of the Brexit Build Up ?
https://www.irishcentral.com/news/politics/attacks-northern-ireland-no-deal-brexit-extremists