... The God tells Abraham that his descendants will spread throughout the world and he will be the father of great nations. He also convinces Abraham to leave his home land and go to Canaan. Consequently, Jews start living there and continue to spread. But doesn't this mean the conquest of others' lands? Why would the God choose exactly Abraham and assure him to take the land of others? It seems too political to be spiritual.
P.S. I just want to understand why it simply happened so.
12:1 God said to Abram, 'Go away from your land, from your birthplace, and from your father's house, to the land that I will show you.
12:2I will make you into a great nation. I will bless you and make you great. You shall become a blessing.
12:3I will bless those who bless you, and he who curses you, I will curse. All the families of the earth will be blessed through you.'
15:1 After these events, God's word came to Abram in a vision, saying, 'Fear not Abram, I am your shield. Your reward is very great.'
15:2 Abram said, 'O Lord, God, what will you give me if I remain childless? The heir to my household will be Damascus Eliezer.'
15:3 Abram continued, 'You have given me no children. A member of my household will inherit what is mine.'
15:4 Suddenly God's word came to him: 'That one will not be your heir! One born from your own body will inherit what is yours.'
15:5 He then took [Abram] outside and said, 'Look at the sky and count the stars. See if you can count them.' [God] then said to him, 'That is how [numerous] your descendants will be.'
15:6 [Abram] believed in God, and He counted it as righteousness.
15:7 [God] said to him, 'I am God who took you out of your Casdim to give you this land as a possession.'
15:8 'O Lord, God,' replied [Abram], 'How can I really know that it will be mine?'
15:9 [God] said to him, 'Bring for Me a prime heifer, a prime goat, a prime ram, a dove and a young pigeon.'
15:10 [Abram] brought all these for Him. He split them in half, and placed one half opposite the other. The birds, however, he did not split.
15:11 Vultures descended on the carcasses, but Abram drove them away.
15:12 When the sun was setting, Abram fell into a trance, and he was stricken by a deep dark dread.
15:13 [God] said to Abram, 'Know for sure that your descendants will be foreigners in a land that is not theirs for 400 years. They will be enslaved and oppressed.
15:14 But I will finally bring judgment against the nation who enslaves them, and they will then leave with great wealth.
15:15 You shall join your fathers in peace, and you will be buried at a good old age.
15:16 The fourth generation will return here, since the Amorite's sin will not have run its course until then.'
15:17 The sun set, and it became very dark. A smoking furnace and a flaming torch passed between the halves of the animals.
15:18 On that day, God made a covenant with Abram, saying, 'To your descendants I have given this land, from the Egyptian River as far as the great river, the Euphrates;
15:19 [the lands of] the Kenites, the Kenizites, the Kadmonites,
15:20 the Hittites, the Perizites, the Rephaim,
15:21 the Amorites, the Canaanites, the Girgaes and the Yebusites.
These are the two places (Genesis 12 and Genesis 15) where G-d tells Abraham that his children will become numerous and he will become the father of a great nation.
At no point does G-d tell Abraham to conquer anything. In fact, Abraham PURCHASED the land in question. When Sara died, Abraham wanted to purchase a small plot of land in Hebron, a cave in which to bury his wife. He approaches Ephron, who offers him the plot of land for free. Abraham says that he would rather purchase the land, so that in future generations will not say that he stole the land. Ephron says, well, if you are going to purchase the land, I have to sell you the entire land of Mamre as well, and the cost will be 400 shekels (which was a HUGE FORTUNE at that time). Abraham agreed to the purchase, and the land then belonged to Abraham through bill of sale. (See Genesis 23)
What then happened later, after the Israelites were done wandering the desert, was that they tried to return to their home... A home that was bought and sold legally by Abraham. The people who were there refused to accept that the Israelites were the rightful rulers of the land. They declared war against the Israelites, not the other way around. In fact, with the exception of Amalek, the Israelites were ordered by G-d to offer peace to every nation that lived in the area. If they accepted peace, the Israelites were ordered to live with them in peace. However, NONE of those living on the land, and none of those surrounding the area accepted the peace offers of the Israelites. And THAT was the reason for the wars in question. But there is no doubt that the land itself belonged to Abraham and his decendents.
So in answer to your question, G-d never ordered the Abraham or his decendants to conquer anyone.
Another point... What makes you think that G-d doesn't get involved in politics? G-d has an understanding of human nature that goes beyond anything that man can know. By nature, man is a political creature. Spiritual leaders HAVE to be political leaders as well. Moses was a VERY political creature, for instance. Look at his leadership of the Israelites, his face-off with Korach and his followers, his interventions on behalf of the Israelites with G-d, the criticisms of Aaron and Miriam against Moses. Moses was the ultimate human politician in addition to being the ultimate human spiritual leader. A good pulpit rabbi or church pastor is also a good politician. Anybody who leads has to be a good politician. G-d is the ultimate leader. Therefore, G-d is also the ultimate politician. Leadership in ANY capacity requires political skill.