The medal's obverse bears an allegorical female figure holding a lamp and an olive branch in outstretched arms, standing in front of a globe, clouds below.

The reverse bears four shields on a raised circular panel, at top, U.S. shield, at bottom, the United Kingdom's. Large PAX in center; dates 18 - 15 above, 19 - 15 below; around,  ONE HUNDREDTH ANNIVERSARY OF PEACE AMONG ENGLISH SPEAKING PEOPLES

The design on the obverse is based on a medal by J.G. Hancock celebrating the Treaty of Ghent, which ended the War of 1812. 

The circular medal measures 64.4mm in diameter and was issued by an organizing group called the American Peace Centenary Committee. It was struck in bronze and silver by Tiffany & Co. of New York.  No mintages are reported. 

There is also a smaller diameter medal with a different reverse.

Many thanks to the Numismatic Department of the Yale University Art Gallery for their generosity and support in making this medal available to me for research.

References:   Marqusee 384