  We study of the role of galaxy-galaxy interactions and disk instabilities in
producing starburst activity in galaxies out to z=4. For this, we use a sample
of 387 galaxies with robust total star formation rate measurements from
Herschel, gas masses from ALMA, stellar masses and redshifts from multi-band
photometry, and JWST/NIRCam rest-frame optical imaging. Using mass-controlled
samples, we find an increased fraction of interacting galaxies in the starburst
regime at all redshifts out to z=4. This increase correlates with star
formation efficiency (SFE), but not with gas fraction. However, the correlation
is weak (and only significant out to z=2), which could be explained by the
short duration of SFE increase during interaction. In addition, we find that
isolated disk galaxies make up a significant fraction of the starburst
population. The fraction of such galaxies with star-forming clumps ("clumpy
disks") is significantly increased compared to the main-sequence disk
population. Furthermore, this fraction directly correlates with SFE. This is
direct observational evidence for a long-term increase of SFE maintained due to
disk instabilities, contributing to the majority of starburst galaxies in our
sample and hence to substantial mass growth in these systems. This result could
also be of importance for explaining the growth of the most massive galaxies at
z>6.
