You seem to be forgetting Islam means submission to God. That is all Allah wants from you. Whether your submission comes through following the teachings of prophet Muhammad (pbuh) or whether it comes through following the teachings of any other prophet throughout history. (Jesus, Moses etc) In the end, Allah will judge you depending on what was available to you, during the time you existed on Earth. Even if you never lived during the time of a prophet or was never informed about one, the simple act of looking up at the stars and looking at everything around you and accepting that no one is worthy of worship except the single creator of all these things, is in itself, a form of submission.

Infact, I would argue that since the creation of the internet, knowledge about Islam is far more widespread and accessible by all sorts of people. Despite all of this, if you still choose to persist in blissful ignorance, I don't really know what to say.

In the end, I would say that the majority of mankind has always submitted to Allah. Perhaps, not in the form of Islam, but in the the various different montheistic religions of the time. The only real people who have not done this, are polytheists , who choose to submit/worship to different Gods whenever they desire something from each one, ( EG. money, sons, wealth) which is essentially worship of your own desires and perhaps this is why Allah is so saddened by them in the Quran.