A false flag is a covert operation that stages an attack and frames another country or group for carrying it out. The attack may be real or a hoax. Here are a few examples:
A retired Turkish general named Sabri Yirmibeşoğlu admitted that Turkish forces burned down a mosque on Cyprus in the 1970s and blamed it on their enemy. He explained: “In Special War, certain acts of sabotage are staged and blamed on the enemy to increase public resistance. We did this on Cyprus; we even burnt down a mosque.”
Russian spies were caught planting live explosives in the basement of an occupied apartment building in Ryazan, during the 1999 Russian apartment bombings. The bombings raised the approval ratings of Vladimir Putin and justified the second Chechen war.
The Indonesian military killed two American teachers in Papua in 2002 and blamed the murders on a Papuan separatist group.
Former Indonesian president Abdurrahman Wahid says police or the military may have planted one of the bombs in the 2002 Bali nightclub bombing.
In 2002, Macedonian police staged a terrorist attack on themselves. They claimed that Al Qaeda terrorists opened fire on them, and they had the dead bodies of the terrorists to prove it. In fact, the bodies were of seven illegal immigrants that the police had trafficked into the country and then murdered.
In July 2001, at the G8 summit in Genoa, police planted two Molotov cocktails and faked the stabbing of a police officer, in order to justify a violent crackdown against protesters.
Between 2002 and 2010, the Columbian military murdered thousands of Columbian civilians. Bodies were dressed up as rebels to make it appear as if they had been killed in combat. Colonel Luis Fernando Borja was one of those convicted.
The head of Saudi Arabian intelligence, Prince Bandar, blackmailed Russia by threatening Chechen terrorist attacks at the 2014 Winter Olympics.
See here for the historic list of false flags (website is not endorsed).