Yes becouse we all suck their balls.

Every embassy is guarded by a military unit from that particular country. So that's not an issue. However, hosting an entire military installation, something that goes well beyond necessary diplomacy, is an issue to carefully consider. Should war break out between the US and Russia, the radar site in Czechia would be a target, but not practical grounds for a full invasion. The Russians would just get a surgical airstrike to destroy the radar or a long range missile. Russia has many of those. However, if the Czechs were to host a full US military base… well, then that's grounds for having your territory be a legitimate part of the battlefield.