[SwellJoe]

Most contracts have "through no fault of the undersigned" waivers in them. i.e. acts of god or government are often covered in some way within the contract language, making parties not liable for hurricanes and changes in law that cause contracts to become null. There's probably some kind of responsibility in these kinds of cases, but it's not going to fall under the usual termination of contract terms. And, whatever responsibilities that exist can be difficult to enforce without the state backing up the wronged party.

Edit: Which is why investors often choose not to invest in companies based in countries that have a history of economic or political instability. It can be difficult to hold someone to their obligations after investing if the state itself isn't going to consistently side with the rule of law. Russian and Chinese investors, for example, were they not already dealing with an even more unpredictable state, would possibly choose not to invest in the US because of unpredictable relations. But, most international investors consider US law to be predictable and stable and safe for investors.

[commandar]

A valid contract can't compel one of the parties to engage in illegal activity, can it?

[SwellJoe]

In international contracts, the activity might be legal under one state but illegal under another. Which law applies? Without some reasonable language to cover it, I guess one could end up with one party to the contract between a rock and a hard place. Their legal entity in one nation bound by a contract in that nation, with their legal entity in the other nation bound by the laws of the land. I don't know the intricacies of all of this, but I suspect things could get ugly without some defined behavior built into the contract in such instances.