Modern

While it is easy to dismiss the actions that arose from Macbeth's greed because of the feudal and violent time in which he lived, one can not overlook the similarities with the 20th century.
Macbeth has become a symbol for leaders who take control of a government and then fortify their hold on power by eliminating opposition to them, often through violent methods.
The best example would be of the former leader of the Soviet Union: Joseph Stalin.  After gaining power Stalin, like Macbeth, was overcome with greed and the need to retain this power and to strengthen his hold on it. It was his grip on power that made him lose touch with the principles that he had originally held, just as Macbeth lost touch with the honour and loyalty he once had. Again with parallels to Macbeth, Stalin tried and executed any and all who opposed him, including former friends and allies.
Control from greed can also occur in democratic governments when elected officials lose touch with the people who elected them and then eliminate through violence or legislation any opposition.  Hitler is an example of this, as a democratically elected president who took control of what would become the most devastatingly evil organization the world has ever known.
Other instances when democracies have become dictatorships that have occurred in the last five years alone are Milosevic's control over Yugoslavia and Hitler like elimination of ethnic Albanians in Kosovo and Sharif's former control over Pakistan.