There was a 50% increase in "arrests and plots linked to domestic Islamist extremism" in the United States during 2019, according to data compiled by the Anti-Defamation League's Center on Extremism.Thirty of those arrests were connected to domestic Islamist extremism, nine of which were designated as "terror plots." The ADL reports that seven of the "terror plots" were being devised by home-bred United States citizens.According to the ADL, a portion of the 2019 plots focused on targeting religious institutions such as churches, synagogues, mosques and community centers. "In the last several years, America has experienced an increase in targeted violence against our faith-based communities and organizations," Department of Homeland Security Acting Secretary Chad Wolf said in December. The ADL added that, "While there has been a significant uptick in white supremacist attacks targeting places of worship, including the Charleston church shooting, Pittsburgh Tree of Life Synagogue shooting, and the Poway synagogue shooting, Islamist extremists have also targeted religious institutions."The Islamic State of Iraq and Syria (ISIS) has shown affinity for these types of attacks in the past. The most recent example occurred last year, when it claimed responsibility for the bomb attacks throughout Sri Lanka on Easter Sunday that killed 321 people, in what officials believe was retaliation for assaults on the mosques in New Zealand the month before.The Christchurch attack, which was broadcasted live on Facebook, saw a lone gunman armed with semi-automatic weapons target Muslims attending Friday prayers in Christchurch, New Zealand, on March 15, 2019. The shooting became New Zealand's worst peace time mass shooting, killing 51 worshipers. That attack also consistently appeared to be a main motivator behind many of the thwarted US domestic terror plots.Out of the nine terror plots, one of them planned to target the busy walkways of the National Harbor in Maryland. Another focused on the Israeli consulate in New York – as well as tourist attractions found throughout the greater New York area, such as the Statue of Liberty – and an additional plot was directed toward the White House. Separate plots focused on a church in Pittsburgh, a white supremacist rally in California and college campuses around Florida. The ADL notes that antisemitism has long been "at the core of Islamist extremist ideology," with three of the thwarted 2019 terror plots, devised by US citizens, point directly to that notion's validity.In January 2019, 23-year-old Hasher Jallal Taheb was arrested after planning to attack the White House and Statue of Liberty in part of what he claimed “was his obligation to engage in jihad.” He later added that his potential targets included the Washington Monument, the Lincoln Memorial and an unnamed synagogue. The attack was believed to be inspired by al-Qaeda ideology, after he "sent his two presumed collaborators a link connected to Anwar al-Awlaki, the former al-Qaeda in the Arabian Peninsula leader," according to the ADL.In April, 26-year-old Mark Steven Domingo received what he believed to be a working explosive device that he intended to detonate at a white supremacist rally, "after considering other targets including 'Jews, churches and police.'” Domingo noted in multiple video manifestos that "there must be retribution" for the Christchurch attacks, adding that if ISIS came to the US, he would swear his allegiance to them.And in May, 20-year-old Jonathan Xie attempted to provide support to the Palestinian terrorist organization Hamas by attacking a “pro-Israel march" with the intention of shooting "everybody” in attendance, adding apathetically that “you can get a gun and shoot your way through... all you need is a gun or a vehicle to go on a rampage.”While there were no actual attacks or murders directly linked to domestic Islamist extremism last year, the ADL still laid down a stark warning:“Make no mistake: the threat of Islamist extremist activity in the United States is serious and cannot be ignored,” said ADL CEO Jonathan Greenblatt. “In 2019 alone we saw nine individuals arrested for planning attacks on US soil and a total of 30 arrests linked to domestic Islamist extremism. We are deeply grateful for the efforts of federal and local law enforcement to investigate and disrupt these potentially dangerous attacks.”The other 21 arrests stemmed from charges against individuals engaging in criminal activity prompted by Islamist extremism. A "large majority" of the constituency allegedly provided "material" support to ISIS. Approximately 70% of the arrests were attributed to or inspired by ISIS.“ISIS’s ability to continue inspiring a large percentage of violent activity even after being effectively disbanded demonstrates the lasting influence of its violent ideology and propaganda on Islamist extremist activity in the United States,” said Oren Segal, Vice President for ADL’s Center on Extremism. “As long as the ideology persists and spreads online, extremists will continue to be inspired by violent rhetoric and instruction.” While none of the planned US domestic plots actually transpired, a Saudi Air Force second lieutenant killed three people and wounded eight others in December during an unexplained shooting rampage at the US Naval Air Station in Pensacola, Florida, where he was training. The FBI later revealed that the shooter, Mohammed Alshamrani, was most likely inspired by al-Qaeda to commit the act of terror.Reuters contributed to this report.