When H II Regions are Complicated: Considering Perturbations from Winds,
  Radiation Pressure, and Other Effects
  We explore to what extent simple algebraic models can be used to describe H
II regions when winds, radiation pressure, gravity and photon breakout are
included. We a) develop algebraic models to describe the expansion of
photoionised H II regions under the influence of gravity and accretion in
power-law density fields with $\rho \propto r^{-w}$, b) determine when terms
describing winds, radiation pressure, gravity and photon breakout become
significant enough to affect the dynamics of the H II region where $w=2$, and
c) solve these expressions for a set of physically-motivated conditions. We
find that photoionisation feedback from massive stars is the principal mode of
feedback on molecular cloud scales, driving accelerating outflows from
molecular clouds in cases where the peaked density structure around young
massive stars is considered at radii between $\sim$0.1 and 10-100 pc. Under a
large range of conditions the effect of winds and radiation on the dynamics of
H II regions is around 10% of the contribution from photoionisation. The effect
of winds and radiation pressure are most important at high densities, either
close to the star or in very dense clouds such as those in the Central
Molecular Zone of the Milky Way. Out to $\sim$0.1 pc they are the principal
drivers of the H II region. Lower metallicities make the relative effect of
photoionisation even stronger as the ionised gas temperature is higher.
