Sanctions are generally cheaper to implement than a full scale military campaign.
They have a long term, corrosive affect on a countries economy. Often reducing a large part of the population to a miserable, impoverished existence. If the country has big cities and an industrialised economy it frustrates the ambitions of the most articulate and educated and that may put the political leadership under pressure for economic reform. Especially when they compare themselves to neighbouring countries that seem to be prospering.
But if the population lives mainly in rural areas, living off the land and is largely uneducated, it has less affect. If the population is isolated, indoctrinated and the dictator has spies everywhere and big army. Then they live in a bubble and know little else. So it is with North Korea.
The Iranians I have met feel the effect of sanctions very acutely. Iran is also a big country and historically a major regional power. It also has Oil so there is always a deal that can be done.
Sanctions against a country work best if it does significant trade with the rest of the world. Some countries simply do not. The US, for much of its history did not rely on international trade, it had lots of land and resources. Conversely the UK, in common with other European states was always a ‘trading nation’.
Wartime blockades are different thing, a military strategy to starve the enemy.
Sanctions are an economic strategy to put pressure on a country to negotiate if they want to benefit from trade.
It is a viable alternative to a war. Imposing sanctions on Iran that hobbles its economy and puts its leadership under pressure. The alternative: an invasion with massive military power. Well that is what happened in Iraq.
Russia is invested in international trade and it is a big Oil and Gas exporter so there is scope for sanctions. The US as a big gas exporter stands to profit from being an alternative source of supply.
The alternative is a confrontation between nuclear powers and a potential WW3.
The invasion of Ukraine must prove to be a hugely expensive mistake for Russia and sanctions can help with that. I am sure Russia does not want to become as cut off from world markets as Iran.
There are, however, some serious difficulties. Putin has a lot of reserves to fall back on and Russia is a well establish Gas supplier to Europe since Soviet times. There is a big dependency of Russian natural gas in Europe and that will take years to change. So sanctions targeting Russias major export will be a two edged sword unless the US increases the volume of LNG it sells to the European market.
I am sure there are a lot of calculations going on at the moment about what can an cannot be done. The US, UK and EU will be making announcements shortly.
I am pretty sure the big football match in St Petersburg will not be happening.