The Paris terrorist attacks Friday night left 129 dead, including one American, with 350 people injured and now the world is left wondering where the next attack will come.
As French President Francois Hollande vowed merciless revenge and British Special Forces patrol U.K. streets, U.S. cities have also increased their security measures to protect Americans from possible terrorist attacks.
Police in Washington D.C., New York, San Francisco, Chicago, Miami, Los Angeles, Boston and other major American cities have increased patrols and stepped up security efforts after the Paris terrorist attacks.
Although federal officials haven't reported any credible threats, U.S. Secretary of Homeland Security Jeh Johnson told NBC News, police were taking extra security measures out of an abundance of caution.
"At this time, we know of no specific or credible threats of an attack on the U.S. homeland of the type that occurred in Paris."
French experts, however, warn this is only the beginning and a new war on terror will see American casualties. French terrorist authority and former judge Jean-Louis Bruguiere told the New York Times, America could be a future target.
"We've taken a huge hit. Today we are unfortunately considered the principal enemy. This is only the beginning. We've entered a new phase that is going to resemble September 2001. And the U.S. will be hit."Philadelphia Police Commissioner Charles Ramsey told USA Today that increased patrols would secure the city's transportation center and historic sites, as well as provide security for Sunday's NFL game.
"Obviously, one of the targets in Paris was a sports stadium. We're not taking any chances."American sports leagues also increased security measures in the wake of the Paris terrorist attacks with the NHL, NBA and college sports teams all taking increased precautions. The NFL, however, isn't taking any additional measures to keep fans safe during Sunday's games, spokesman Brian McCarthy told USA Today.
"Security at our games is always at a heightened state of alert."Security has been stepped up at French sites across the country including the French Consulate and historic sites. Boston's Logan airport also remains on high alert.
With public spaces, tourist attractions, airports and federal building under increased security, U.S. presidential candidates are stepping up their rhetoric against ISIS and international refugees.
Republicans Donald Trump, Ben Carson, and Ted Cruz urged Obama not to accept the planned 10,000 refugees from Syria, while Jeb Bush said an effort to destroy the West is under way.
Many presidential candidates are calling for increased U.S. military action against ISIS, which has taken credit for the horrific terrorist attacks in Paris.
Until now, the U.S- led war against ISIS has done little to halt the organization from grabbing power.
The self-styled caliphate that suddenly came to power after grabbing huge swaths of territory in Syria and Iraq has been focused on seizing territory and expanding its reach, but the last two weeks have demonstrated its chilling capability.Days before the synchronized attack on Paris killed 129 people and injured 350 more, ISIS terrorists attacked Beirut in retaliation for their increased military activity. A Russian passenger jet was also shot down over Egypt after damaging air strikes.
Former President George W. Bush advisor, Frances Fragos Townsend, told the New York Times, ISIS clearly has ambitions beyond its own borders.
"ISIS is absolutely a threat beyond the region. We must not continue to assume that ISIS is merely an away threat. It clearly has international ambitions beyond its self-proclaimed caliphate."[Photo by Christopher Furlong/Getty Images]