"Major" is somewhat fuzzy, but for now I'm thinking 20 killed OR 100 injured.
Last one per wikipedia would have been in 2017, so per Laplace rule of succession prior should in some sense be 1/(2025 - 2017 + 2) = 10%.
References:
https://www.politico.eu/article/uk-police-arrest-terror-probe-iran-terrorism-investigations/,
https://www.telegraph.co.uk/news/2025/05/04/iranian-terror-attack-uk-hours-away-from-being-launched/,
https://en.wikipedia.org/wiki/Terrorism_in_Europe#Deadliest_attacks
Update 2025-05-06 (PST) (AI summary of creator comment): The creator has clarified that the primary criteria for an event to resolve this market are:
It is a terrorist attack in Europe.
It results in 20 killed OR 100 injured.
An event meeting these criteria will count even if it is not listed on the specific Wikipedia page (Terrorism in Europe#Deadliest_attacks) that was referenced in the original description (in the context of baserate calculation). The 2024 Magdeburg car attack was provided as an example of such an event that would count.
Update 2025-11-15 (PST) (AI summary of creator comment): An attack does not need to be officially charged as terrorism to count for resolution. Any attack that meets the criteria (20 killed OR 100 injured) will resolve this market positively, regardless of whether it is prosecuted as terrorism.
1,000@LukeShadwell Any attack that fits the criteria
My read is that the knife attack doesn't hit the 20 deaths or 100 injuries threshold, but if it had this would have resolved positively.
Ten people were wounded in a stabbing attack on a train in Cambridgeshire, England, on Saturday by two suspects who brutally set upon terrified passengers with huge knives — and anti-terror investigators are probing the incident, according to reports.
Mmh, <https://en.wikipedia.org/wiki/2024_Magdeburg_car_attack> wasn't in the wikipedia list, but would count, so the baserate should be higher.