Alliance - (Easton's Bible Dictionary)
A treaty between nations, or between individuals, for their mutual advantage.
Abraham formed an alliance with some of the Canaanitish princes (Gen. 14:13), also with Abimelech (21:22-32). Joshua and the elders of Israel entered into an alliance with the Gibeonites (Josh. 9:3-27). When the Israelites entered Palestine they were forbidden to enter into alliances with the inhabitants of the country (Lev. 18:3, 4; 20:22, 23).
Solomon formed a league with Hiram (1 Kings 5:12). This "brotherly covenant" is referred to 250 years afterwards (Amos 1:9). He also appears to have entered into an alliance with Pharaoh (1 Kings 10:28, 29).
In the subsequent history of the kingdoms of Judah and Israel various alliances were formed between them and also with neighbouring nations at different times.
From patriarchal times a covenant of alliance was sealed by the blood of some sacrificial victim. The animal sacrificed was cut in two (except birds), and between these two parts the persons contracting the alliance passed (Gen. 15:10). There are frequent allusions to this practice (Jer. 34:18). Such alliances were called "covenants of salt" (Num. 18:19; 2 Chr. 13:5), salt being the symbol of perpetuity. A pillar was set up as a memorial of the alliance between Laban and Jacob (Gen. 31:52). The Jews throughout their whole history attached great importance to fidelity to their engagements. Divine wrath fell upon the violators of them (Josh. 9:18; 2 Sam. 21:1, 2; Ezek. 17:16).