Terror attacks don’t rattle markets like they used to

Tuesday's terror attacks in Brussels were a grim reminder of our cities' vulnerability in the age of global travel. But there's evidence that investors have become inured to their effects as attacks in the West become more common.

The German DAX index closed up 0.42 percent Tuesday; a decade ago it's doubtful it would have gone up.

An analysis of market performance before and after terror attacks over the past decade suggests that investors don't react as drastically as they once did.

For example, the DAX fell more than 3 percent in five days in March 2004, after the Abu Hafs al-Masri Brigade killed more than 190 people on the Madrid train system. Last November, the DAX reacted to the attacks in Paris by climbing 2.3 percent over five days.

In the immediate aftermath of Tuesday's attacks, traders worried about the effects on the market. Initial reactions showed European investors seeking cover in traditional safe havens like gold and government bonds.

Compounding that, recent debates around border security and Syrian migrants have threatened to rend the European Union itself.

But it seems as if markets recovered quickly from the initial shock, and European markets closed mixed. U.S. indexes opened down but rose for gains bymid-morning. The S&P 500 was up 0.2 percent by mid-afternoon.

In the past five years, the post-attack market reaction has gone from an overall -0.5 percent return to a median gain of 2 percent over the ensuing five days. After the Paris attacks in November, the Euronext 100 index was up 2.4 percent.

Some strategists think it's a new era as Europe and the U.S. work through isolationist impulses and the spread of migrants from an unstable Middle East. A market reaction could be some ways off, said Jason Trennert, Strategas Research's chief investment strategist.

"I think globally there is clearly a re-evaluation of immigration policies," Trennert told CNBC's "Squawk Box." "There's no question that nationalistic tendencies and populist tendencies are going to get stronger," which could make trading more difficult.