A couple of months ago I wrote an article about how Buddhist ethical first principles commit Buddhists to probably political anarchism. The basic argument was simple: According to Buddhism, to even begin to practice, one must accept the Five Precepts. The first two are "to abstain from taking life" and "to abstain from taking what is not given." But by definition, the state must violate these two in order to exist, because laws require force, and ultimately deadly force, for their enforcement, and any taxation that isn't voluntarily simply is taking what is not given. Thus Buddhists, when they use the state to advance their political goals, are violating the very core of their professed ethics.
One objection people have made to my argument is that the Buddha, while speaking to various rulers during is life, didn't tell them to abandon rule, and didn't tell them that the very nature of government violates Buddhist ethics. Given that the Buddha understood Buddhism as well as anyone, this disconnect means I must be mistaken in my interpretation of his teachings.
I'm skeptical. I can think of at least three plausible reasons why the Buddha wouldn't have publicly spoken to the disconnect between political action and personal ethics.
1. The Buddha taught to his audience.
First, in the vast body of writings known as the Pali Canon, which is accepted by Buddhists as the earliest extant record of the words of their philosophy's founder, we see the Buddha teaching conflicting doctrines. The traditional explanation for this is that the Buddha was supremely practically minded. His goal was to help others achieve an end to their suffering, and so he taught to the individuals he happened to be speaking to at the particular time. He told each person what they needed to hear in order to progress toward enlightenment, and given that different people have different needs and are in different situations, his teachings varied.
Generally, kings don't take well to being told their rule is illegitimate. If, upon sitting down with a king, the Buddha said, "If you want to follow the Dharma, you must cease enforcing your will through laws and you must cease taxing your subjects," it's rather unlikely the conversation would've gone any further, any opportunity to help this person achieve release from samsara precluded.
It is possible, then, that the Buddha decided to focus, in his talks with rulers, on matters he knew they'd be more receptive to, in keeping with his general pedagogical strategy.
2. The Buddha was dependent on rulers.
Mendicants in the Sangha begged for everything. A monk owned only his robe and his alms bowl. The Buddha had no lands, no source of income, no army for his defense. If a ruler grew angry and decided to snuff out his nascent movement, there was little the Buddha could've done to stop it. Thus keeping his mouth shut about the incompatibility of ethics and state rule was simply prudence. He could do more good in the world teaching the Dharma, even if it meant staying quiet about politics, than he could dying at the hands of an irritated monarch.
3. The Buddha never fully analyzed the nature of state power.
We know the Buddha was at least somewhat aware of the concerns I raised in my essay. In the sutta SN 4.20, while sitting in private retreat, he asked himself,
I wonder if it’s possible to rule legitimately, without killing or having someone kill for you; without conquering or having someone conquer for you; without sorrowing or causing sorrow?
Of course, the answer to his question, at least as it regards all governments then existing and all governments that have existed since, is "No." It is impossible to have a state that makes and enforces laws without at least the threat of violence, including killing, of those who disobey the law. Otherwise laws are nothing more than suggestions.
But the Buddha lived far before philosophers had adequately mapped out the nature of state power or questioned its moral legitimacy. Then, and even now, the assumption was that state power is legitimate, and the only question worthy of analysis was how to properly use it. Attempts to offer an origin of this power existed, but it was only recently that philosophers began to seriously question its very legitimacy or to poke holes in the standard justifications.
I find it quite plausible that the reason the Buddha didn't tell rulers that their very rule itself violated the first two precepts is simply because he hadn't adequately examined the nature of that rule. Like everyone else of his time, he assumed its existence, and couldn't imagine an alternative. (Except possibly in the mythical form of the Chakravarti, or Wheel Turning Monarch.)
That the earliest philosophers, of which the Buddha was one of the most important, didn't have the benefit of the 2,500 years of philosophical development and progress we do shouldn't be held against them. But we also shouldn't fail to recognize that such progress exists. We simply have thought more deeply about these concepts over the last two thousand years, and so know more. Just as the Buddha held to primitive medical beliefs, he also held to primitive political ones, and part of that takes the form of not thinking through the political implications of his underlying ethics.
Fortunately, the rest of us can now do that for him.