This looks like something which a tabbing environment can solve
\documentclass{article}
\pagestyle{empty}
\begin{document}
\begin{tabbing}
480-479: \=Battle of Thermopyle\\
\>Greek Victories at Salamis and Plataea end Persian war
\end{tabbing}
\end{document}

Alternatively, you can use tabular.
\documentclass{article}
\pagestyle{empty}
\begin{document}
\begin{tabular}{lp{4in}}
480-479: & Battle of Thermopyle\\
& Greek Victories at Salamis and Plataea end Persian war
\end{tabular}
\end{document}

The spacing is a little bit different, but then you don't have to battle with extraspace before and after the environment. Also, this later approach will let you use longtable that can span multiple pages.