I was trying to close vote this question. What were the races of the horses in Mahabharata?
Under the option of "off topic because..."--"relates to another stackexchange site"---- only 'Meta' site is listed. So I could not select "History.stackexchange.com" site.
How do I do that?
Meta appears because there is a migration path to meta - if enough users vote that the post belongs on meta, it will be magically sent there. These migration paths are not available for all sites, because since migration is a rather drastic irreversible action it is not considered a good idea to give normal users such easy access to it. See the link for more information on this.
What you can do is leave a comment under the question saying it should be asked on another site, and vote to close as off topic. OP can simply delete and re-post, which is cleaner than migration. You can also flag for moderator attention and ask for the post to be migrated. If there is no migration path to a site, only mods are able to migrate questions there.
However, just because a question is on-topic (or even better suited) on one site does not mean it is off-topic on another. We should not vote to close questions as off-topic unless they are really out of scope. The question you linked to seems perfectly fine and on-topic to me, though I am a newbie here and maybe I'm wrong.
