Especially since he had mixed feelings on the subject, anyway. On the one hand, he thought the Polish situation did not lend itself well to military solutions. On the other hand . . .

Who could say for sure? The old saying "you can't export a revolution with bayonets" certainly had some truth. But a lot of it was just wishful thinking, too. Mike had read a great deal of history since the Ring of Fire, and one of the things he couldn't help notice was how often history was shaped by the outcome of wars. Napoleon was often denounced as a tyrant, but the fact remained that many of the revolutionary changes he made were not overturned after his defeat—not even by those he'd defeated and forced to accept those changes.

So . . . There was no way of knowing the outcome of a war between the USE and Poland. If was possible, in the event of a clearcut USE victory, that serfdom in eastern Europe would be destroyed. Not by Gustav Adolf and his armies, maybe. But one thing you could be sure of was that Gretchen Richter and her Committees of Correspondence would be coming into Poland on the heels of those armies. And they hated serfdom with a passion.

--1635 The Eastern Front

Even if all Rumata has are a few history books and overwhelming weaponery, he should be able to make some solid improvements in the social organization. And if he has the full backing of a spacefaring civilization, he should be able to do a lot.

I haven't read Hard to be a God (it does sound interesting), but my proposal:

• First enough productive giveaways that there's a surplus worth speaking of. It has to exist before the people can keep it.
• Then establish and protect a communications network. One armored internet terminal per tavern, perhaps. Create forums the powerful can't sensor. Publish some history and organization textbooks so that people get used to the idea that better things are possible.
• Declare some meta-laws, like due process, no ex-post-facto, public jury trials... Make them mild enough that rulers consider them acceptable. Enforce them ruthlessly.
• Publish relevant science and technology books.
• This should be enough to see the beginnings of a middle class. Place them under your protection.
• Whenever there's a succession crisis (those are common) declare a republic in the region. Crush any attempt to end it violently using overwhelming force. At first, you'll need to do a lot of work teaching people how to have a republic and enforcing things, but you should be able to back off as they learn.

Basically plagiarize shamelessly from the nicer parts of history and keep your eyes open for how to use what you have.