I'm looking at a linear regression model using the data on wars in the 20th century. There are two time variables on the right-hand side: 1) year and 2) a dummy variable that equals 1 if a war occured after 1945. My question is: what is the coefficient on this dummy really telling us? It doesn't seem like a valid counterfactual to say: "holding all other variables (including year) constant, what is the effect of going from a pre- to a post-1945 era?"

Thanks in advance for your help. Also, I'm new here, so please let me know if this post is more appropriate in some other section of the forum.