Liaison: communication or cooperation which facilitates a close working relationship between people or organizations.
Most intelligence services maintain liaison relationships with other intelligence services. These relationships serve several purposes: You can obtain intelligence information from two intelligence services cooperating than from only one; Some intelligence services have better sources of information in areas that another service might find helpful; In their own country, intelligence services have better sources and greater capabilities. By maintaining a close, working relationship, an intelligence service can piggyback on those capabilities and use them where they might normally not have that ability. As an example, if I wanted to keep an eye on the Russian Embassy and intelligence presence in a foreign country, it would be easier and more efficient to use the surveillance capabilities of the host country.
Another sort of unspoken reason to conduct liaison is to gain access to the intelligence officers of the opposite service and try to recruit them. Any intelligence service worth its salt will recruit penetrations of other intelligence services so they can report on activities that are harmful to the recruiting service. You always want to know if your personnel are being targeted by another intelligence service. So far, so good.
Some of these liaison relationships are well known and have been publicly acknowledged. The Fives Eyes, composed of the U.S., UK, Canada, Australia, and New Zealand springs immediately to mind. We have excellent relationships with the Jordanians and numerous European services. We don't try to recruit penetrations of Western liaison services because, as democracies, the things we would be interested in knowing about these countries are carried on the front pages of their newspapers. However, dictatorships tend to be different.
Over time, these liaison relationships gave the CIA Chief of Station (COS) considerable power. (The Chief of Station is the individual in charge of all intelligence operations in a particular country. He or She is thus the senior CIA officer in that country.) The COS could draw upon the resources of the host nation's security service or services to not only conduct intelligence operations but also influence operations and covert action. In some countries, the COS had more influence and contact with the host country's government, including the leader, than the State Department. When senior CIA officials visited some of these countries, the COA could arrange meetings with the President or King of the country, and have the host country throw lavish receptions and dinners for the visitors. In the eyes of senior CIA leadership, the COS was important, a power to be recognized. In some countries, they helped execute U.S. foreign policy. The COS could get things done through the liaison service that could not be done through normal diplomatic channels.
Soon, the liaison relationship became supremely important. Not only could things get done, but these relationships made the COS look good, helping further career advancement. Many COS's avoided anything that could damage that relationship. That included recruiting penetrations of the host country service, fearing that if such a recruitment attempt were discovered, the close relationship would end. Eventually, stations began to rely on liaison to provide information on what was going on in the country. In authoritarian countries, the CIA avoided contact with opposition members, people that were against the government, because the liaison service would be angry at any contact with what they viewed as the enemy. The CIA swore by liaison intelligence reporting. They were our friends. They would tell us the truth. This blinded the CIA.
A good example of the dangers of relying too much on liaison is Iran in the 1970s. Prior to the Iranian revolution, the CIA and other U.S. government agencies, such as the Defense Department, had very close and cozy relations with various Iranian government agencies. Iran was the linchpin of the U.S. government's national security policy in the Middle East. We were turning Iran into a military and economic powerhouse. The CIA's close relationship with the Iranian security service, SAVAK, was particularly important. However, it came at a price. The CIA, and other U.S. agencies, avoided developing relationships with members of the opposition in order to avoid angering SAVAK and the Shah, who ruled Iran with an iron fist.
When the Iranian Revolution came in 1979, the CIA and the U.S. government were blindsided. They were surprised at how powerful the discontent against the Shah was, how serious the movement was, and how rapidly it came about. The intelligence community as a whole had little coverage and few sources on what was going on in Iran. It was an intelligence disaster.
Unfortunately, what happened in Iran in 1979 is not uncommon. To this day, many COS's see their relationship with liaison as not only critically important for U.S. intelligence operations, mostly true, but also critically important for their careers. In the early 2010s, when the people of several Arab countries became fed up with dictatorship and corruption and began large-scale protests against their governments, later called The Arab Spring, the CIA was caught by surprise. We had no idea how potent the movements were and the threat they posed to long-time U.S. allies. Much of this failure--certainly not all, but most--was due to the heavy reliance on liaison in these countries. The danger still continues and I can think of several countries where we would have no idea about internal opposition given our overreliance on liaison.
One of the first things I was taught when I joined the CIA was there are no friendly liaison services. This doesn't mean that all liaison services are hostile. What it does mean is that, like the CIA, liaison services answer to their government first and foremost. While many of these services are extremely helpful and even critical to the CIA's intelligence mission, they have their own national security interests. These will always come before U.S. national security interests. We all pay lip service to this fact, but too often we don't actually take it to heart.