Terrorist attacks in Brussels (May 2014) and Paris (January and November 2015) highlight the threat related to the arrival of foreign fighters (FFs) from civil wars elsewhere. We develop an argument suggesting that terrorism at home is systematically affected by the exit of the so-called FFs out of civil wars abroad. We contend that foreign civil conflicts ending in success for rebel groups can result in a surplus of well-trained FFs, increasing the risk of terrorism at home. By contrast, when rebel groups are defeated in foreign civil conflicts, we anticipate a restriction in the flow of FFs, which reduces the likelihood of terrorism at home. Empirical analyses on most countries for the years 1970 to 2006 support these hypotheses. Our tests also demonstrate that the flow of FFs is associated with the creation of new terrorism campaigns rather than the exacerbation of existing operations.