What is a conspiracy? To act together by design is one interpretation. Some times you could say that there are "systematic", a result of bureaucratic systems, laws, regulations and acts that have been place in the public and some having secret classifications.
They have certainly been conspiracies in the United States. The reason for conspiracies are various, some are to achieve a secret agenda, which is positive for those that initiated the set of events. Others are there to hide official criminal or illegal activities, some of these activities are deemed in the interests of "national security", which is a very dubious term, and criminal activities with in the government system itself, usually for self interest purposes.
Conspiracies by there very nature, are hard to pin down, unless there are witnesses willing to expose such activities, or a paper trail which indicates or exposes the conspiracy. There are examples which have been exposed which have been officially confirmed, the Pentagon Papers scandal is one, and the famous Watergate incident is another.
You will find that those that conspire try to divert the attention away from the purpose, the existence, and those responsible for such activities. They can be in the form of finding a fall guy or group or even organization, to take the blame for the results of such conspiracies. Or blend it in the "background" so it seems nothing has happen , and no conspiracies have occurred.
One thing I have not mentioned is this. Those in power can create internal security instructions, which could even be time managed, which allows such activities to occur, such as suspending constitution rights, and domestic laws. These certain activities which would normally be a violation of the constitution and laws, would be allowed to occur. Obviously some form of law is followed in some of theses circumstances, others activities would be goal orientated, means to an end. Some of these occurrences would be in secret thus could be considered a conspiracy.
I can safely say conspiracies will occur in the future for political, national security, criminal, and manipulative purposes, and many for large goals, and personal gain.