You can use arrow keys to navigate in the map.
Where would the taxes go? Normally taxes go to a governing body, but a global governing body that enforces a global tax would compromise national sovereignty.
assumingly you'd probably try to distribute it on a fair level. you could do this based on national produce, based on the amount of citizens etc.
You get rid of tax havens.
Every country who would bail out of the deal would be favored by big companies, making it a tax heaven again. You would have to force every country into the deal.
You could in addition to this(due to the majority of nations agreeing on a global tax system(assumingly)) ensure that some form of punishment would take place for corporations moving outside of that system.