Problems with importing posts

I’m in the middle of importing a massive number of posts from one WP site to another which is kinda working, well sort of…

In any case I’m now trying to consolidate the posts under the appropriate category/s and wonder if there is a bulk method for recategorizing categories?

I first tried renaming a category first so that it matched the category of the site I’m importing to but that didn’t work (eg 205 Afghanistan posts = 205 new Afghanistan (1,2, etc categories added! )

Deleting the added categories should in theory add them to the default but then I still have to go through every post and change the category anyway!

Any solutions to this would be greatly appreciated as I have over 7000 articles to incorporate.

Bill