Each soldier is checked by elite Muscovite guards before being permitted to enter. With the rise of the merchants, one can never be to careful. There has also been lots of terrorist attacks before the revolt. This was never released to the international republic due to wanting not to scare other nations. It was believed to be contained, but they have finally found the source of the attacks.
After finding suspected illegal weapons (such as matchlock) upon some of the Wainriders, they are either to go through intense security or sent back to Rhun. The Prince is on the fence for this at the moment.