Abstract We investigate the causes underlying the decline in the government expenditure multiplier after the Korean War, through the lens of a structural dynamic stochastic general equilibrium model. We estimate the model using Bayesian methods and annual frequency data from 1939 to 2017. The model replicates the observed fall in the expenditure multiplier. We find that the decline is accounted for by changes in two of the model’s structural parameters, namely a decline in consumption habit persistence and a higher autocorrelation of the public expenditure processes. These changes imply a stronger negative wealth effect, a lower discretion of US fiscal policy and, consequently, a multiplier of smaller magnitude. The model identifies the news shocks to military spending, yet fiscal news plays little role in the decline of the multiplier. Rather, the news shocks account for an important fraction of medium-term variances of debt and military expenditures, which justifies their inclusion in the model.