Finding the joint range of values is one way with adding in a little flexibility.
SeedRandom[12345];
data1 = RandomVariate[NormalDistribution[0, 1], 100];
data2 = RandomVariate[NormalDistribution[5, 3], 200];
(* Get minimum and maximum of all datasets combined *)
{xmin, xmax} = MinMax[Join[data1, data2]];
(* Allow for some flexibility *)
xlow = xmin - 0.1 (xmax - xmin);
xhigh = xmax + 0.1 (xmax - xmin);
Histogram[data1, Automatic, PlotRange -> {{xlow, xhigh}, Automatic}]
Histogram[data2, Automatic, PlotRange -> {{xlow, xhigh}, Automatic}]
