Edited and reposted. Check my profile for an actual explanation.

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Ten little countries standing in a line.
Poland saw a pony and then there were nine.

Nine little countries outside the gate.
France went in and then there were eight.

Eight little countries trying to get to heaven.
Holy Rome made it and then there were seven.

Seven little countries eating Trix.
Lithuania ate too much and then there were six.

Six little countries praying Germany won't arrive.
Italy saw him and then there were five.

Five little countries wanting to soar.
America managed it and then there were four.

Four little countries sipping tea.
England sipped too much and then there were three.

Three little countries playing peek-a-boo.
Japan forgot Canada and suddenly there were two.

Two little countries playing with a gun.
Denmark was shot and then there was one.

One little country sitting in the sun.
Norway found Iceland and then there were none.