Hi,
I would think that people with British ancestors will find some members of their family were involved within the Armed Services at sometime due to the British Empire and Britains involvement in the two World Wars.
There are many sources to check if a member of your family had served in the military but it maybe an idea to first concentrate on the first and Second World wars because vast numbers of the population enlisted or were conscripted. Service and pension records of non commisioned soldiers (First World War) are available for a fee to view online via Ancestry. These documents are amazing with all sorts of details on the person and his involvement during the war but sadly 60% of these documents were destroyed during the Blitz.
The Second World War service records are held by the MOD and due to data protection the next of kin must complete an application form to request these documents.
Another well known provider is in the process of making available soldiers' military pension records from 1760-1911 which covers the Napoleonic wars onwards and in the resource centre there is further details.
It maybe an idea to talk to family, friends check photos' or old documents for relatives involvement.
I have no idea of the information or process for soldiers of the Commenwealth eg. Australia, New Zealand and Canada etc.
If you want to post some family members names and places of birth born from 1879-1899 I could do a general search to attempt to find any matches for the First World War. You maybe surprised how many of your relatives may have served during the Great War
When I get the chance I will create a list of useful military websites in our resources section.
Regards
Adrian