They were tyrants. Genghis was known to pile huge piles of heads after sacking cities. He could not have known God.
Opportunities are open for people, and it is the choice they make, that God judges.

they were all used by satan in his plans

God knows Ghengis Khan. He knows Napoleon, Ceasar and Hitler too. But they did not know Him.

They most likely weren't Christians (I am assuming by god you mean the Christian God).

I have no idea if they did or not.Either way they are all dead now.I focus on reaching live people for Christ.

No he wasn't Christian. But Genghis Khan did allow Religious freedom in his Empire, something which was practically unheard of at the time.

not being a "christian" in the accepted word all i can say is that some of these so called tyrants are sent in to a situation to carry out some deeds or other to move along humanity at large. I insist that reincarnation is a fact of life men such as the above are perhaps more evolved than the general public and have the energies and dispositions to make a bad scheme better, or to bring to heel something that for a long time needs changing . a difficult subject indeed but who was Hitler eg. he was a second degree initiate a psychic too who aligned himself with the dark forces to instigate the second world war along with some 7/8 other dark guys.at the same time Churchill was here to counteract this force. it was indeed a great battle that had to be seen to be upon this physical plane. indeed there was much destruction but God is both the creator and the destroyer too, there is no satan and Lucifer is a great white angel that obeyed God and did his work. there are many such instances of great souls yes great indeed that take on weird roles to our minds, many are the unsung heroes in our midst. you do not have so long to wait now for the greatest of them all to appear to all men. the world teacher Lord Maitreya. use your search engines now.amen and om shantih

Anyone in power is put there by God. That doesn't necessarily mean that they worshipped or obeyed His laws.

1 Samuel 2:6-10 – The LORD kills and makes alive…The LORD makes poor and makes rich. He brings low AND LIFTS UP. He raises the poor from the dust and lifts the beggar from the ash heap to set them among princes…For by strength no man shall prevail. The adversaries of the LORD shall be broken in pieces…He will give the strength to His king, and exalt the horn of his anointed.

Exodus 9:16 — But indeed for this purpose I HAVE RAISED YOU [Pharaoh] UP, that I may show My power in you, and that My name may be declared in all the earth.

Isaiah 44:24…28 — Thus says the LORD…Who says of Cyrus, 'He is My shepherd, and he shall perform all My pleasure, saying to Jerusalem, "You shall be built," and to the temple, "Your foundation shall be laid."'

Isaiah 45:1…4 — "Thus says the LORD to His anointed, to Cyrus, whose right hand I have held–to subdue nations before him and loose the armor of kings. 'I will go before you and make the crooked places straight…I will give you the treasures of darkness and hidden riches of secret placed, that You may know that I, the LORD, who call you by your name, Am the God of Israel. For Jacob My servant's sake, and Israel My elect, I have even called you by your name; I have named you, THOUGH YOU HAVE NOT KNOWN ME."

God Bless