The Failure of Sanctions

I'm intrigued by the continuing use of sanctions in the modern world. Sanctions seem to be a popular way to impose some sort of punishment on evil states. But do sanctions actually work?
The US imposed sanctions on Japan to prevent oil and steel entering Japan in response to Japan's occupation of Manchuria in the 1940s. The sanctions failed to free Manchuria from occupation and dragged the US into WWII. The sanctions on Cuba have forced them to abandon their communist ideology - oh wait, after decades it hasn't. In 433BC Athenians imposed sanctions on Megara for farming sacred land. The sanctions eventually dragged Athens into the disastrous Pelopennisian War with Sparta, which it finally lost after decades of debilitating warfare. The historical record of using sanctions for political purposes is a dismal failure.