> Making a mandatory 18 YO conscription would be silly in a "real
> world". Just getting the new regulation to everyone would be
> difficult; no radio, no
> newspaper, no huge government bureaucracy.
There actually is a medieval comparison with conscription in the
late 14th and 15th centuries in England and Wales. Laws were passed that
made it illegal to play sport on a Sunday and all good yeoman had to go
and shoot the longbow for at least two hours. This made archers freely
available for the crown during the hundred years war and introduced the
concept of the yeoman into society.

This law was apparently universal and provided troops for Henry
the V for his invasion of France. Already trained at no extra cost the
English and Welsh troops were the turning point in many battle.

In Birthright terms this probably is a decree followed by a
deduction of one point of loyalty from any province this is impossed on
permantly until the law is changed (would you like it if the law said
you couldn't do what you wanted on your day off). It would however give
you the advantage of getting archers instead of levies.