Analysts at Citi just released two notes in the aftermath of the brutal attacks in Paris, looking at both whether the violence marks a change in strategy for ISIS , and what the stock market reaction might be if that's the case.

The authors, led by chief global political analyst Tina Fordham, see the attacks on Paris as part of a recent and concerning change of strategy from the group.

Referencing the attacks on Beirut, the downing of a Russian passenger jet and the Paris attacks together, here's what the note says :

Such a series of successful attacks on targets aligned with countries at war with IS in Syria suggests a new front in the conflict, with IS moving beyond fighting in Syria and Iraq to extending the theatre of war beyond its "caliphate."

An email from analysts at Barclays has a similar tone, noting that the threat from the group around the world is "intensifying and spreading."

They're more negative about the possible macroeconomic shocks the change could cause, given the fact that the European economy is already so weak:

Any comparison with previous terrorist attacks such as in Madrid in 2004 and in London in 2005 is not necessarily relevant.

Attacks against civilians in a European country are likely to weigh on consumer confidence, a major risk in a situation where the main driver of growth in Europe is consumer demand, with other components of demand still very subdued.

In Citi's second note, the authors assess how stocks have reacted to acts of violence at home and abroad in the past. In short, there are often sharply negative moves in the short term but, US stocks have "rebounded rather quickly" from incidents abroad.

The Yom Kippur war in 1973 aligns with a much deeper crash, but not precisely because of the actual violence.

In the aftermath of the war, the major oil exporters in the Arab world coordinated an oil embargo, cutting production and sending prices up around the world.

On average, the impact of wars and acts of terror seems pretty muted in the long-run, with stocks actually rising significantly on average a year after the event.