In the following sentence, what relative pronoun should be used?
The United States supported Pakistan, ______(who or which) on the other hand didn't change the law.
In this sentence, you are talking about the governments of these two countries, so you would use "which' (though I'm unclear what the sentence actually means.)
Note, though, the following sentence:
England, who were all out for 109 on day one, came back on the second day of cricket to take...
Here, we are referring to the English cricketers, and so "who" is used. This is common when using the name of the country, or city, when talking about sport. I can't off-hand think of anymore exceptions such as this.