I was doing research on the mars missions and came across a timeline on the Malin Mars Space Sciences website detailling the joint missions between the US and Russia occuring between 1992 through 1999.

Then there's a shift and there's only US missions to Mars from 2000 on...

I've found research on Russian missions from the 60s to the 90s, but then it's like it just disappears on the mars scene.

My question is what happened to these martian joint missions/cooperation between the US and Russia? Politics (with the changes in government?) Lack of Russian resources for these projects?