The FTSE, DAX and CAC all fell sharply the same session Brent crude broke back above $100 a barrel. The connection is obvious. It's also not confirmed by any single source.
London's FTSE 100 closed down 1.38% on September 9, a decline one market-commentary source described as leaving the index at six-week lows after opening the session with modest gains. The selling was worse elsewhere on the continent: Frankfurt's DAX fell 1.62% and Paris's CAC 40 dropped 1.97%.
Coverage of the session describes the selling as broad and continental, and characterizes the synchronized decline as pointing to a shared macro concern, without naming a specific trigger. The same trading day, Brent crude settled above $100 a barrel for the first time since July, following the latest escalation in the US-Iran tanker conflict, and US equities and Treasury yields moved in tandem with that story.
The timing lines up. Whether it explains the size of the European move is a separate question that same-day coverage does not answer. An oil-driven equity selloff would typically hit energy-import-dependent European economies harder than a diversified US market, which is broadly consistent with continental Europe underperforming Wall Street's own decline that day. But that is an inference drawn from the timing and the relative magnitudes, not a causal claim made by any outlet.
For investors trying to size European equity exposure to Gulf-conflict risk, the practical takeaway is that the linkage is plausible and the magnitude was real, even though nobody covering the session on the day was willing to put a name to the cause.