As a rule of the sequence of tenses, the Guide to Grammer and Writing says:
"When the main clause verb is in the past or past perfect, however, the verb in the subordinate clause must be in the past or past perfect. The exception to this rule is when the subordinate clause expresses what is commonly known as a general truth."
Based on this rule, is the following sentence correct?
He said in his speech that participants will offer economic assistance, which will increase trade and investment, if North Korea agrees to dismantle all of its nuclear programs in a verifiable manner.
I am very confused. Please explain to me.
The clauses that you think are subordinate clauses are actually independent clauses. Independent clauses in a complex sentence can be in any tense as long as their relationship to the main clause remains clear.