Western countries and their interests overseas remain prime targets for international terrorist groups like the Islamic State of Iraq and the Levant (ISIL) and Al Qaida. Al Qaida’s founder Usama bin Laden, and his successor Ayman al Zawahri, identified a number of countries as allies of the US and so legitimate targets, including the UK, Australia, France, Japan, Norway, Poland and South Korea. Al Zawahiri cited as justification their actual or claimed involvement in conflicts in Afghanistan, Iraq and Chechnya or their support for Israel.
There are many reasons a terrorist group may consider a country to be a potential target for attacks. ISIL, for example, considers any countries which have supported military action against the group to be legitimate targets. As well as seeking to direct attacks against these countries, ISIL frequently uses its social media to inspire low sophistication attacks by extremist supporters worldwide on generic "Western" interests.
Terrorists often try to attack official personnel and property, such as diplomatic missions and military forces. Notable incidents include shootings at the Canadian Parliament in Ottawa in October 2014, the shootings at various army venues around Chattanooga, USA in July 2015 and the shooting of a policeman in Australia in October 2015. Terrorists target the police and military as they easily associated with the state, and their public-facing nature makes them fairly accessible for low sophistication attacks.
However, terrorist cells also target less well-protected places frequented by Westerners. These could include locations where crowds gather such as social and retail venues, tourist sites and transport networks (rail, road and airports). This was illustrated by the attacks in Bali in October 2002, Madrid in March 2004, Egypt in July 2005, Mumbai in 2008, Nairobi in 2013 and Paris, Tunis and Sousse in 2015. The effectiveness of randomly targeting a public place comes from the likelihood of low security and the element of surprise. Depending on the location, public venues also offer the chance for maximum casualties. This was demonstrated in the November 2015 attacks in Paris.