The Modern idea is that Madagascar was first settled sometime around 700 AD by shipwrecked Indonesians. This seems fairly easy to avoid. Madagascar is far from Indonesia and it wouldn't seem hard to prevent a shipwreck. The next people who settles there were Omani Traders and East Africans. To stop this you need to weaken trade in East Africa. I do not know how to do this, but it must be possible. No Omani traders and the East Africans would have no reason to sail out and eventually find the island. Once it is discovered by Europeans, who would settle and claim it, and how would this affect history? Secondly, how plausible is it for Europeans to first settle Madagascar?