Last month, Kuwait banned entry to anyone from Syria, Iraq, Iran, Pakistan and Afghanistan. The government said the ban was temporary, but was needed because too many Islamic radicals and gangsters were trying to enter Kuwait from those countries. This sort of problem is nothing new for Kuwait.
It's mostly about Iran. Increasingly, over the last six years, Kuwait has had problems with Iranian attempts to operate spy and terrorist cells inside Kuwait. A year ago, Kuwait broke up an Iranian terrorist cell of about 15 people. Some of the cell members were Kuwaitis, including a few who had served in the security forces. Others were Arabs from neighboring countries. The police raids seized documents, weapons, communications equipment and $250,000 in cash. These guys were well equipped, and apparently well paid. This cell was formed and sustained by Iranian intelligence operatives. The arrested spies admitted that they visited Iran frequently as tourists, where they received training and money. Smugglers brought in some equipment, but much of what the cell members needed (like weapons) they could buy on the black market in Kuwait.
Iranian agents like this are usually recruited from among the Shia (who are half the population) in Kuwait, and then trained in Iran. The Iranian networks consist partly of "sleeper cells" (agents who are inactive, and go about their normal lives until activated by their Iranian bosses.) Kuwait is still trying to discover the extent of the Iranian networks, but fears that it may be a large one (with several hundred, or even several thousand members). The cell busted last year was detected mainly because it was active. The sleeper cells are the most worrisome, as these would be activated if Iran were to want to put a lot of pressure on Kuwait. It's because of the Iranian threat that Kuwait maintains such close military relations with the United States.
After last year's crackdown, Kuwaiti police noted that Iranian supported Islamic radicals were often able to enter Kuwait from other countries, most frequently Syria, Iraq, Pakistan and Afghanistan. Thus the recent ban on visitors from those countries.