Complex sentence: These five states are known to have detonated a nuclear explosive before 1 January 1967 and are thus nuclear weapons states under the Treaty on the Non-Proliferation of Nuclear Weapons, they also happen to be the UN Security Council's permanent members with veto power on UNSC resolutions.
Split into simpler sentences: These five states are known to have detonated a nuclear explosive before 1 January 1967 and are thus nuclear weapons states under the Treaty on the Non-Proliferation of Nuclear Weapons. They also happen to be the UN Security Council's permanent members with veto power on UNSC resolutions.