One country one king or PM or president :) and there are many countries in the vessel world and with different main requital and the reliance requital. Similarly to Buddha lands as well on teachings suitable to one's requital.
vessel world (器世間). The living environment of a sentient being, e.g, a birdcage keeping a bird. In the karmic rebirth of this sentient being, assuming the life form of a bird is the main requital (æ£å ±), and the birdcage, its vessel world, is the reliance requital (ä¾�å ±).
My understanding is that in India then, there were many high level of Theravada practitioners that can not achieve a breakthrough. When Buddha Sakyamuni attained enlightenment at that period, he delivered the Theravada teachings to liberate them first and subsequently, bring them into Mahayana as most of them were Mahayanist capacity. All Buddhas just provide the teachings like medicine to cure different deluded illness.
Similarly to three periods of the Dharma, all sentient beings also carry with them the different capacity.
As for Amitabha Pureland - Buddha Sakyamuni land recommended and all Buddha as well - 一切诸佛所护念� in Amitabha Sutra, and Buddha Amitabha is the King of all Buddhas in Sutra of Infinite life. Another awesome fact about Pureland is that all the 4 abodes are true nature or supreme enlightenment.
three periods of the Dharma (æ£åƒ�末期). The Dharma of ÅšÄ�kyamuni Buddha will end after the three periods: (1) The true Dharma age (æ£æ³•) lasted 500 to 1,000 years after His passing. During this period, there were teachings, carrying out of the teachings, and attaining of fruits. (2) The Dharma-likeness age (åƒ�法) lasted 500 to 1,000 years. During this period, there were teachings and carrying out of the teachings, but no attaining of fruits. (3) The Dharma-ending age (末法) will last 10,000 years. During this period, the teachings will gradually vanish, and there will be neither carrying out of the teachings nor attaining of fruits. Because people will no longer be receptive, the Dharma will be gone for a long time until the advent of the next Buddha. In the Bodhisattva in the Womb SÅ«tra (CBETA, T12n384, 1025c15–19), fascicle 2, the Buddha prophesies that, after 56 koá¹i and 70 million years, which (if a koá¹i is 10 million) means 630 million years, Maitreya Bodhisattva will descend from Tuá¹£ita Heaven and become the next Buddha, bringing the Dharma to a renewed world.