Peaceful demonstrations are part of democracy. The first amendment of the constitution of America states that Congress can make no new law hindering the right to peacefully assemble.
Congress according to the constitution can make no new law hindering the right to peacefully assemble. This does not prohibit officials of states and cities from controlling demonstrations. A city can request to know from those that want to demonstrate the reason for their demonstration and the place in which they want to demonstrate. It is not against the constitution to control peaceful demonstrations. If a city will deny a group of people to demonstrate, these people can go to the courts to receive permission.