Complex sentence: Mexico is one of the few countries which has capabilities to manufacture nuclear weapons but has renounced them and pledged to only use its nuclear technology for peaceful purposes following the Treaty of Tlatelolco in 1968.
Split into simpler sentences: Mexico is one of the few countries which has technical capabilities to manufacture nuclear weapons. However it has renounced them and pledged to only use its nuclear technology for peaceful purposes following the Treaty of Tlatelolco in 1968.