This morning's bombings in London were horrific, but they shouldn't distract investors from a few core strategies, Jim Cramer said on his "RealMoney" radio show Thursday

Cramer discussed the best trading responses to this morning's subway bombings in London's public transport system. Early in the show, he put aside the notion that the U.S. market's afternoon rally makes American's "unfeeling" or "uncaring."

"Exogenous events will always play roles in the market," said Cramer. "But after 9/11, the notion of terrorism as an event that can wreck our markets has forever changed."

Traders recognize terrorism is part of life, Cramer said. They need to be able to decide quickly what sectors it will affect. "And if it does not look like a sector will be affected, then we step in and buy."

Today was a good chance for U.S. buyers as European traders beat down shares ahead of the U.S. open. Cramer partly attributed the European response to profit-taking, saying "our markets have not been as robust as the Europeans so they have more profits to take."

Any additional fallout will be positive, in Cramer's opinion, as the British have traditionally been tough on terrorism.

Cramer said he used this morning's weakness to buy the tech and defensive stocks that the Europeans were dumping. In other words, he nibbled at semis and aerospace names.

On the other hand, he moved out of bank stocks when they rallied later in the day.

"I'm astounded that the Fed did not blink at all when I was on vacation," said Cramer, who has been away for about a week. A lot of bank stocks have been buoyed by their high yields recently, but another two rate hikes means that cash will be more attractive. So he advised swapping out of the banks.

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