Onedog: My memory is getting a bit hazy, but I think the chronology is something like this.
Hilton US sold the international hotels to Howard Hughes/TWA. These hotels were eventually bought by Ladbroke, a UK gaming company.
Ladbroke operated its own hotels in the UK. These became Hilton National hotels (a ragbag of mixed standards) while the more upmarket hotels in the UK cities became Hilton International hotels. Hilton US's international hotels were branded Conrads as they weren't allowed to use the Hilton name outside the US.
Hilton hotels in the US and outside the US had different logos and branding as well as different reservations systems.
Some 3 years ago (?), somebody knocked commonsense into the two groups' heads, and they ended up sharing branding and reservations systems. The international properties joined HHonors.
The non-US properties (including those in Canada) are still part of Ladbroke, though that company has been renamed Hilton Group plc. There is speculation that Hilton Group (the UK company, remember) will dispose of its gaming interest and concentrate on hospitality.
There is also longstanding speculation that Hilton Hotels Corp and Hilton Group will one day become one.
Hope this helps.