Brexit

This whole issue of the UK leaving the EU presents some interesting ideas that may be more viable than they otherwise would have appeared.  The United Kingdom might no longer be very "united" if Scotland and Northern Ireland vote to separate from them.  Other countries might leave the EU as well.  But the more interesting application is in the US.  Although many state constitutions reserve that right, there are no written rules at the federal level for how a state withdraws from the union.  There was a proposed constitutional amendment in 1860 to ban withdrawing, implying that it would otherwise be allowed.  But the Civil War laid the issue to rest at the time, establishing very strong precedent against it.  So how would it have to happen now?

I have long thought that it would be wise for each state legislature to ratify a constitutional amendment to allow states to withdraw after a percentage (50/60/66/75 take your choice) vote of the population and/or legislature.  Even if the states involved had no plan to actually withdraw, it would give them leverage when negotiating with the federal government, and curb the unhindered expansion of federal power.  Once 75% percent of the legislatures had ratified it, it would be law without involving Congress, the president, or the Supreme Court.  It would bypass all of the DC gridlock, and return power to the states.  The first step in that process is a Convention of States, which is currently being actively pursued by certain political groups.  The only reason state legislatures might hesitate to ratify that amendment (which gives them more power and leverage against the Federal government) is that they might fear other states actually leaving, and weakening the remaining union.  But I see no other way of reversing the exponential increase of federal government expansion and intrusion, short of revolution or civil war, which I believe is best to avoid.