SPAM is unsolicited mail delivered to you, wasting your time and consuming resources. This applies to both physical mail and electronic ones (email).
While you're typically protected by laws against physical SPAM to a certain extent, email is uncontrollable and has been on the rise ever since it started some time in the 1990's.
Many preventative measures have been taken throughout time to fight email SPAM, but it has only worked on marginally classifying and separating your email from SPAM.
One should ask: Why do we keep receiving SPAM? How come it never stops?
A simple answer is that it's being funded!
The rise of malicious software known as worms has given the option for mischievous companies or groups to take control of thousands of user machines and use them to send SPAM to millions of users around the world.
Those shady companies or groups are charging money to promote products of other companies. Mostly drugs but may include promotions to other products.
A simple conclusion is that if you penalize companies that pay for shady groups to use such abusive methods, SPAM would almost disappear.
If governments that house such companies refuse too cooperate, ISPs worldwide can contribute to major SPAM reduction by making it a national law to ensure that your computers at home and company are clean.
ISPs can monitor traffic patterns and identify malicious traffic, after that, it should be obliged to notify users that are suspected to be infected and as such, those users must clean their machines or be fined, and if they don't comply, inflate the fine and so on.
When taking such measures, governments allowing shady companies to operate and pay for SPAM groups to run can be blacklisted, by blocking all IP addresses from that country.
This has another powerful side effect: When blocking IP addresses of a whole country, businesses in that country will be severely affected and will demand law enforcement of criminalizing the offenders responsible for SPAM and those funding it.