The Marcionite temptation is old: cut the Old Testament loose, keep the gentle Jesus. The Church rejected that in the 2nd century, and for good reason — the same God who thunders at Sinai is the God who weeps at Lazarus's tomb.
What's actually in the text
Most Old Testament violence is described, not prescribed — Cain, the judges' cycles, David's wars, Israel's exile. The narrative consistently shows violence as the wound, not the cure. The Law actually restrains violence compared to its Ancient Near Eastern neighbors (limited retaliation, sabbath rest for slaves, protection for foreigners and widows).
The hard texts
The conquest narratives (Joshua, 1 Samuel 15) are the hardest. Paul Copan and others note significant warrant-language hyperbole common to ANE military rhetoric, judgment on specific Canaanite practices (child sacrifice), and the consistent biblical pattern that Israel itself faces the same judgment when it does the same things. (See our entry on the Canaanites for more.)
The Orthodox lens
The Fathers — Origen, the Cappadocians, Maximus — read the Old Testament Christologically. Every story is reaching for the King who would not destroy his enemies but die for them. St. Maximus calls this the "logos" within each event: the meaning Christ unveils.
The Cross is the lens. A God who would rather be killed than kill is not the author of casual violence — he is its undoing.
A pastoral word
If a passage troubles you, sit with it; don't dismiss it or sanitize it. The Church has been reading these texts for two thousand years with Christ in view. Bring your question to a priest, a good commentary, and the Liturgy. The God you meet there is the God of Sinai and Golgotha — and he is good.