With no explanation, label each line with "location-GPE", "O", "event-attack/battle/war/militaryconflict", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart" or "building-airport" preceded by ":".
In
the
mid-to-late
nineteenth
century
,
the
westward
expansion
of
pioneers
created
a
powder
keg
in
the
form
of
crowded
Native
American
tribes
and
nervous
white
settlers
.
In:O
the:O
mid-to-late:O
nineteenth:O
century:O
,:O
the:event-attack/battle/war/militaryconflict
westward:event-attack/battle/war/militaryconflict
expansion:event-attack/battle/war/militaryconflict
of:O
pioneers:O
created:O
a:O
powder:O
keg:O
in:O
the:O
form:O
of:O
crowded:O
Native:O
American:location-GPE
tribes:O
and:O
nervous:O
white:O
settlers:O
.:O