If 10,000 screaming hordes of Islamonazis start to blow up England and capture grade schools, I would be all for increasing the size of our military with a draft.
Such a reality exists, even if it is quite small. Any American who would resist the call to arms for such a holy war, 21st century crusade, or World War IV, would just as soon give up.
in such an eventuality, any able-bodied male between 18 and 45(?) can be called up as part of the militia as defined in US code.
anyone who failed to volunteer to fight in such a circumstance... I wouldn't want him at my shoulder on the lines.