It is not surprisingly Americo-centric for a post titled "How Islamic terrorists reduced terrorism in the US". I acknowledged that there was a bigger (numeric) fall in terrorism in the US in the 70s. The fall in the US after 2000, though, is probably as big or bigger when expressed as a percent drop rather than as an absolute drop. Equal efforts at reducing a variable results in drops that are similar by percentage more than by absolute number. (That means the effort to go from 100 cases per year to 10 is more similar to the effort to go from 10 to 1 than to the effort needed to go from 900 to 800.)
There has been no fall in terrorism worldwide; just the opposite. It was at its lowest point in 1971-1975, and is over 10 times as high now (as measured by GTD incidents). For Europe at a whole, it was at its lowest in 1970, then was high from 1976 to 1997. For "(USSR & the Newly Independent States (NIS))", there was no terrorism until 1989 (imagine that!), then a steady rise until 2010. The fall I pointed out for the US after 2000 also happens in a graph for Western Europe, which I would expect, but not for the world as a whole.
There is a sudden dramatic fall in Central America bottoming out in 1998, to just a few incidents per year. This might be due to a similar thing happening with the drug wars there, or might just be bad data.
Maybe, the total number of incidents rises just because with the spread of the Internet and other communications technologies, it's easier to get information about terrorists attacks. For example, there definitely were terrorist attacks in USSR before 1989(https://en.wikipedia.org/wiki/Category:Terrorism_in_the_Soviet_Union), but they aren't mentioned in GTD.
Yesterday I was using the Global Terrorism Database to check some suprisingly low figures on what percentage of terrorist acts are committed by Muslims. (Short answer: Worldwide since 2000, about 80%, rather than 0.4 - 6% as given in various sources.) But I found some odd patterns in the data for the United States. Look at this chart of terrorist acts in the US which meet GTD criteria I-III and are listed as "unambiguous":