Before mankind knew of God?

God tells us, "All of mankind will know my name " or "Know me".  Remember, before mankind even wrote "The Holy Words" of God, they had to believe in something. But, let me plant this thought in you psyche, and run with it, if you dare: 

We know that "GOD claims to have always existed, correct?  My challenge is, not many , if any, can comprehend the premise that God always existed, and if we accept any form of life, we have to accept that "something or some entity" had to create it?  Something had to be in control to bring us to any point or form of life.  If not, this was all by accident, and what created "accident"? 

But beyond that, Let's try to comprehend that "God always existed" and I suggest that mankind cannot comprehend that term, ALWAYS.  because, we only know time.  Another words, what was before time? 

If God always, ALWAYS existed, then are we that small to think that there are not , now other forms of existence?  Are we that finite not believe that this entity, GOD, existed in infinity forever, alone and without some other form of existence?  

Told you our minds couldn't comprehend the term "ALWAY". Try it yourself.

Yes, and even those primitive people recognized the need for God, so they worshipped one thing after another, and later invented "gods" to worship. You really can't blame them, since the one true God had not yet revealed Himself to humanity. Now, no-one has that excuse.

Romans 2:14-15 answers that question.

There were totaling to 124,000 Prophets , whom GOD send down all of them to teach mankind in believing in the Oneness of  GOD , the Lord of the worlds , in all nooks and corners of the earth, from Adam ,the first Prophet, right down to Muhammad, the last Prophet of GOD (May GOD be pleased with them all) lasted up till now around 12,000 years and this only religion of GOD shall continue till the end of time.

People all over the world had intact cultures that worked for them. Their cultures were fractured and confused by the introduction of foreign cultures and religions. The Jewish cultute had its own religion that worked for them. Jesus tossed a monkey wrench into that one. Then Christianity became a religion of conquerors and exploitors. What a mess!

The human body is provided to us only to know God. Otherwise, there is no way to know God in the darkness. 

Israelites are followers of Archangels not one God. 

What you describe is related to a few of the reasons for atheism, and is a reason to be skeptical of a religion and for people declining in organized religion and religiosity.

Religions are molded and twisted a bit to come up with answers of faith. One of the core principles in the subsects of the Judao-Christian-Muslim umbrella is that everybody else is wrong. YOUR precise religion is the RIGHT one and everyone else is on the wrong path and belief set.

Since a newborn that dies knows nothing of God, it's innocence has not sinned and goes to heaven. Expand on that if it solves your puzzle to the extent you need it.  

"Neanderthals" never existed.  The first people were Adam and Eve.  And all people can be saved by believing in the Lord Jesus Christ.  The Lord will get the truth to everybody that wants the truth, so everybody is without excuse.  Acts chapter 10 is an example of this.  Nobody can be good enough to avoid hell.  So to avoid hell, believe in the Lord Jesus Christ. It is that easy.  When a person dies, they will be in heaven or hell, and they can't get out of hell if that is where they go.  To go to heaven and not go to hell, believe in the Lord Jesus Christ, without adding any of your works.  Believe in the Lord Jesus Christ, who is God and who died on the cross and shed His blood to pay for all our sins, and who resurrected from the dead.  See Romans 4:5 and 1 Corinthians 15:3-4.

My thoughts are that you have hit upon a very significant problem with Christianity.

they all went to hell for not believing in god. not knowing isn't an excuse for not believing.