AFAIK, not many (none?) will cover you for any, terror related attack.
There are a quite a number of insurance companies that will cover you for travel in countries/regions that are included in government advisories, but it really is necessary to read the policies/check with the companies as there are broadly two categories of cover for such trips:
(a) you have normal insurance for medical/accident, etc, but not for the specific events that are the reason for the government advisory (eg if government advisory is to avoid because of risk of cross border insurgency, you are not covered for that, but would be for any other accident/medical issue, etc). In the case of Uganda, I would say this kind of policy is okay because the real risk of such attacks is really very small indeed, but you are covered for malaria/road accident/mauled by a lion, etc, which are obviously more likely to happen.
(b) all risk, including for what the government advisory is for. I don't know much about this kind of policy, but generally there would still be some exclusions and probably they ask exactly what countries and would not insure for some regions, eg if you fancied some birding in Syria or something.
My credit card, more or less, includes the first kind of insurance - no restrictions on which countries or regions, no restrictions regarding government advice or not, but pretty sure warfare and terrorist activities not covered.
