the government can guard against terrorism only in the United States

The national security system in the United States against terrorism is called Homeland Security. Homeland Security was established after the bombing in New York, New York on September 11, 2001.

Perhaps. Terrorism isn't something that should be tolerated, regardless of whether or not it seems necessary.

Of course, acting against 'terrorism' has resulted in continued conflict and many deaths.

Whether or not the United States should act against terrorism is a subject for debate, and the answer isn't a simple 'yes' or 'no'.

It's really up to the individual to make up their mind. But regardless of whether we should or not, the US seems to be combating it anyway.

Radical Islamist terrorist groups have continued to launch attacks around the world ;)

No, the United States is the worlds largest front runner against terrorism, therefor, the middle eastern countries that support terrorism are not U.S. Allies. This is just one example.