There are a number of systems that measure journal impact factor. SCIMago Journal & Country Ranking (SJR) provides very detailed metrics that cover multiple years at a glance.
In the combined areas of Political Science & International Relations:
SJR reviews roughly 500 journals
JCR review roughly 270 journals
Top 25 Journals in Public Administration
Top 25 Journals in Political Science
Top 25 Journals in International Relations