Through death Jesus destroyed him who had the might of death, that is the Devil.
Jesus used the Devil's own master weapon to oppose the God of eternal life and with it, destroyed the Devil.
The meaning of "destroyed" the Devil is something of a distinct discussion of its own.
For it will be objected - "Well, if by dying Jesus destroyed the Devil, why does the Devil seem to still be around."
The full execution of the Devil's being destroyed requires the cooperation of those who belong to Christ and apply Christ's salvation to themselves. This matter touches on another thread too about sin dwelling in man and the God-men nullifying it by means of Christ living in them - applying to themselves the finished work of Christ.
But I digress a bit.
It appears to me that in eternity "past" God the Creator of all knew within Himself what would be the result of creating sentient beings with their own free will. God knows all. And God had the wisdom to know the potential existed for his creatures to choose of their own freedom that they wanted nothing to do with their Creator.
My belief is that God, in His wisdom, decided that ALL such created creatures who choose to not be under God's authority, He would arrange to be all together under one leader. One creature was created with that potential to act as a reservoir to collect under his authority all other beings who shared his aspiration - to usurp the throne of Almighty God the Most High.
This is one reason why I believe in an ancient universe rather than a young earth. I think that the period of time after creation that this being existed was probably a long time. Perhaps he began to reason that God must be a pushover, a sap, a "not too strong and not too smart" God.
At some time the rebellion began and was headed up by this grand rebel of all rebels. I think God in His foreknowledge let Satan the deputy arch-angel being act as a reservoir around whom all other beings who want to revolt against their Creator, were gathered as one party.
That would include, as far as we know, ancient angels, demonic beings, fallen human beings - ALL
subsumed under one unique and grand sinning and revolting created being.
Death is related to the power of this one. He is said to be the one who has the might of death. God warned the first created humans that if they crossed a certain line of obedience, they would DIE - surely
. And it happened.
"And Jehovah God commanded the man saying, Of every tree of the garden you may eat freely. But of the tree of the knowledge of good and evil, of it you shall not eat; for in the day that you eat of it you shall surely die." (Gen. 2:16,17)
God says the saved are transferred out of the kingdom of darkness (and death) and into the kingdom of the Son of His love.
" Giving thanks to the Father, who has ... delivered us out of the authority of darkness and transferred us into the kingdom of the Son of His love,
In whom we have redemption, the forgiveness of sins; " (Col. 1:13,14)
Death is part of the Devil kingdom from which the saved must be transferred from into the eternal kingdom of the Triune God.