Complex sentence: Republic's fortunes began to decline when the new Cincinnati, Sandusky & Cleveland Railroad bypassed it to make a straight run to Tiffin, although it experienced something of a revival with the coming of the Baltimore and Ohio Railroad.
Split into simpler sentences: Republic's fortunes began to decline when the new Cincinnati, Sandusky & Cleveland Railroad bypassed it to make a straight run to Tiffin. But, it experienced something of a revival with the coming of the Baltimore & Ohio Railroad.