What accounts for the difference in behaviour between the Federal Reserve and the ECB?

The Federal Reserve wants to normalise its interest rates by the end of 2019, while the ECB is planning to raise its interest rates only after the summer of 2019. What accounts for this difference in behaviour between the Federal Reserve and the ECB? Structurally different reactions by the two central banks to inflation and the unemployment rate? Different views at the central banks of the cyclical positions of the United States and the euro zone (does the ECB believe the euro zone is still far from structural unemployment?)? A stronger preference for the present at the ECB than at the Federal Reserve? It seems that the last two explanations are pertinent .