  We reconstruct the evolution of Eta Carinae in the last two centuries, under
the assumption that the two 19th century eruptions were triggered by periastron
passages, and by that constrain the binary parameters. The beginning of the
Lesser Eruption (LE) at the end of the 19th century occurred when the system
was very close to periastron passage, suggesting that the secondary triggered
the LE. We assume that the 1838-1858 Great Eruption (GE) was triggered by a
periastron passage as well. We also assume that mass transferred from the
primary to the secondary star accounts for the extra energy of the GE. With
these assumptions we constrain the total mass of the binary system to be
M=M_1+M_2>~250 solar masses. These higher than commonly used masses better
match the observed luminosity with stellar evolutionary tracks. Including mass
loss by the two stars and mass transfer from the primary to the secondary we
obtain a good match of periastron passages to the two peaks in the light curve
of the GE. Based on these finding and a similar behavior of P Cygni, we
speculate that major LBV eruptions are triggered by stellar companions, and
that in extreme cases a short duration event with a huge mass transfer rate can
lead to a bright transient event on time scales of weeks to months (a
``supernova impostor'').
