The continuity between series is a bit FUBAR.
Originally, Red Alert was a prequel to the Tiberium series.
Then Red Alert 2 came out, and went in an entirely different, cheesy direction. Nonetheless, apparently there was still going to be a connection to Tiberium somehow, or so the original devs claim. (Apparently time travel, Nikolai Tesla, and aliens were involved. Somehow.)
After Westwood was bought out by EA, Red Alert was officially dropped from continuity, making Red Alert and Tiberium into two different continuities. Lots of people still place Red Alert 1 in the Tiberium continuity, since Kane has one scene in it, but it's an amazing one.