Why is "Iranian involvement in the Iraq War" trending?

Wikipedia Overview

The 2003 invasion of Iraq led by the U.S., which toppled Iraqi president Saddam Hussein and his Arab Socialist Ba'ath Party, was the decisive event that allowed Iran to begin exerting an unprecedented level of influence on Iraqi politics. Leveraging the fact that the regime change targeted a rival power and Shia Muslims accounting for the majority of the population in both countries, the Iranian government used Shia militias to serve its interests during the Iraq War. This culminated in a complex series of events from Iran's aiding U.S. coalition efforts to later involvement in the Iraqi insurgency, in which there were instances of Shia militias fighting both alongside and against the Multi-National Force in Iraq. Organizations that enjoyed large-scale Iranian support included the Badr Corps, as well as Kata'ib Hezbollah, Asa'ib Ahl al-Haq, and the Promised Day Brigade. Since 2007, the United States has employed a "kill or capture" strategy with regard to confronting Iranian operatives in the Iraqi conflict.