Interesting stats, but a z-score doesn't really work for time series. It hides the most important part (time-based trends) and can be confusing, which you can see in the comments. Z-scores are designed for looking at the relationship between a number drawn from a sample of similar things. Think "My height vs average height of all people."

There are systematic changes that accrue over time that make, say, 2000 more like 2001 than like 2018. That's what you want to show. A bar chart would have been really interesting here, since the number of terrorist attacks swung wildly from 1,000 to 17,000.