  (Abridged) We investigate the hypothesis that some fraction of the globular
clusters presently observed in the Galactic halo formed in external dwarf
galaxies, by means of a detailed comparison between Zinn's "old halo", "young
halo", and "bulge/disk" sub-systems and the globular clusters in local dwarf
galaxies. The Galactic sub-systems possess distinct spatial and age
distributions, age-metallicity relationships, and orbital parameters, although
we observe some OH clusters with ages and orbits more similar to those of YH
objects. Almost all Galactic globulars with large core radii (r_c) fall into
the YH sub-system, while the OH and BD ensembles are characterized by compact
clusters. The majority of the external clusters are indistinguishable from the
Galactic YH objects in terms of HB morphology, but 20-30% of external clusters
have HB morphologies most similar to the Galactic OH clusters. In addition, the
external clusters have an r_c distribution which very closely matches that for
the YH objects. The old halo r_c distribution can be very well represented by a
composite distribution formed from 83-85% of objects with structures typical of
BD clusters, and 15-17% of objects with structures typical of external
clusters. Taken together our results fully support the accretion hypothesis. We
conclude that all 30 YH clusters and 15-17% of the OH clusters (10-12 objects)
are of external origin. The Galaxy may therefore have experienced ~7 merger
events with cluster-bearing dSph-type galaxies during its lifetime, building up
45-50% of the mass of the stellar halo. Finally, we identify a number of OH
objects which have properties characteristic of accreted clusters. Several of
the clusters associated with the recently proposed CMa dwarf fall into this
category.
