They seem to have an effect upon a country like North Korea, where the sanctions could reach to the power structure of the country.

Otherwise they seem to affect the population and leave the leadership intact and even stronger.

Where they do always work is to give domestic politicians a chance to tell their constiuencies that they are doing something. The sanctions of Iraq, the effort to "get Saddam", did no such thing as "getting Saddam". They caused untold suffering on the people, thousands and thousands of children, among others, starved and made the people dependent upon the government. Meaning Saddam. While quieting domestic demands.

Actually, I don't think the American people supported the Iraqi sanctions. I believe they were in place at the insistence of Western oil companies who wanted to control Iraqi oil. If they couldn't control it, they didn't want it sold.

Sanctions on Cuba simply reinforced Castro's power and created the necessary outside enemy which unifies a country. But they kept the Cuban-American's happy what something was being done.