@article{ref1,
title="Symmetry and Polarization in the European International System, 1870 - 1879: A Methodological Study",
journal="Journal of peace research",
year="1974",
author="Hart, J.",
volume="11",
number="3",
pages="229-244",
abstract="<p>[Abstract unavailable]</p>",
language="",
issn="0022-3433",
doi="10.1177/002234337401100307",
url="http://dx.doi.org/10.1177/002234337401100307"
}