  A far-infrared observatory such as the {\it SPace Infrared telescope for
Cosmology and Astrophysics} ({\it SPICA}), with its unprecedented spectroscopic
sensitivity, would unveil the role of feedback in galaxy evolution during the
last $\sim10$ Gyr of the Universe ($z=1.5-2$), through the use of far- and
mid-infrared molecular and ionic fine structure lines that trace outflowing and
infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni
line shapes and absorption blueshifted wings in molecular lines with high
dipolar moments, and through emission line wings of fine-structure lines of
ionized gas. We quantify the detectability of galaxy-scale massive molecular
and ionized outflows as a function of redshift in AGN-dominated,
starburst-dominated, and main-sequence galaxies, explore the detectability of
metal-rich inflows in the local Universe, and describe the most significant
synergies with other current and future observatories that will measure
feedback in galaxies via complementary tracers at other wavelengths.

Astrophysics of Galaxies