With this supreme knowledge of his, he taught the world what he knew. He taught this way to destroy suffering and there were records of humans who achieved this. Most of them were among monks,some were ordinary lay people(people living a normal lifestyle). These teachings of the Buddha is still applicable for today and it is still practiced in some countries(eg: Sri Lanka).
It is very unfortunate that only a very few in this world has the opportunity to understand the dhamma(buddha's teachings) as it is only for the wise.
The greater danger
The Buddha said that most humans after death are born as animals and in hell. It is so rare that a human being after death will once be born as a human or among the devas(heavenly beings).
The Buddha attained the most supreme attainment of all time, that is enlightenment. That means the Buddha is freed of all defilements(craving,lust,anger,fear etc). Being the one and only person to ever do so, the Buddha had broken the chain of rebirth forever. With this attainment he mentioned that with his divine eye he searched whether there was another being who has ever done this before him, he could not find a single in any world.
All beings born were subjected to suffering
You may not understand this at once if you are born to a rich family, but take a look around you and notice the poor majority. Look at the various kinds of animals, there is always a chance of you being born as an animal.This cycle of rebirh is never ending unless you stop it.