Why would a loving God prefer one nation over another?

A non-Catholic perspective (see @Andrew's answer for a strictly Catholic perspective):
God chose Abraham to be the father of many nations. Note that at this time there was not a Hebrew or Jewish tribe/nation.

Why did God choose Abraham (Abram at the time)?
Genesis 18:19 (Holman Christian Standard)

For I have chosen him so that he will command his children and his house after him to keep the way of the LORD by doing what is right and just. This is how the LORD will fulfill to Abraham what He promised him.

God wanted to display to the other nations how He expected to have a relationship with all people. So long as those descendants (later through Jacob who was renamed Israel) adhered to the rules of the Covenant and later the laws handed down by Moses, the nation(s) would be blessed.

One of the requirements of the covenant between God and Abraham was that of circumcision (Gen 17). Specifically:

Genesis 17:10-14

10 This is My covenant, which you are to keep, between Me and you and your offspring after you: Every one of your males must be circumcised. 11 You must circumcise the flesh of your foreskin to serve as a sign of the covenant between Me and you. 12 Throughout your generations, every male among you at eight days old is to be circumcised. This includes a slave born in your house and one purchased with money from any foreigner. The one who is not your offspring, 13 a slave born in your house, as well as one purchased with money, must be circumcised. My covenant will be marked in your flesh as an everlasting covenant. 14 If any male is not circumcised in the flesh of his foreskin, that man will be cut off from his people; he has broken My covenant.”

So why is circumcision symbolic of the covenant? The answer lies within the New Testament and explains why God would require this of Abraham and his descendants:

Colossians 2:11

You were also circumcised in Him with a circumcision not done with hands, by putting off the body of flesh, in the circumcision of the Messiah.

The point of circumcision is to separate yourself from the rest of the world. God's plan with Israel was to have a nation as an example to the rest of the world. In order to do that, the people must be separated from the rest.

Leviticus 20:26

“You are to be holy to Me because I, Yahweh, am holy, and I have set you apart from the nations to be Mine.”

Beyond circumcision as a sign of separation, it is an even greater tribute to Israel that they were blessed to be the line that would bring forth the Messiah. As all people were at the time, Abraham was of the seed of Eve and there had to be a seed (descendant) to carry out the first Messianic prophecy in the Bible ([see Genesis 3:14-19] for completeness2):

Genesis 3:15

I will put hostility between you and the woman, and between your seed and her seed. He will strike your head, and you will strike his heel.

In light of this, we must be aware that because of God's promise, Satan worked diligently (and still does) to ruin God's plan with Israel. Satan tried but could not stop the birth of the Messiah. And now, through political and demonic machinations, Satan continues to try and destroy Israel to foil the unfulfilled prophecies.

As for a distinctively Catholic view I could not find anything specific to "why God prefer[s] one nation over another."

I can address the second question,

And do other Christian groups share the same view as Catholics?

from the perspective of the theology of Emanuel Swedenborg (1688-1772) and the denominations that accept his theology.

I am not a Catholic, nor am I particularly knowledgeable about the finer points of Catholic doctrine. However, drawing on Andrew's answer above, I gather two general points about God's preference for the nation of Israel over other nations as understood in Roman Catholic theology:

1. Israel was chosen based on Abraham's belief in God as stated in Genesis 15:6 and explained by Paul in Romans 4.
2. Abraham was chosen, not because Israel was to be exclusively God's people, but to be the sign of the gathering of all nations as the people of God, which gathering is the Church (conceived of as the Roman Catholic Church).

Taking the second point first, Swedenborg's theology supports the idea that God's choosing of the nation of Israel was not exclusive, but rather was representative of God's calling to all people, of all nations, to become part of the universal church of God. (Of course, he did not limit that to the Catholic Church.)

Scriptural support for this idea comes, for example, in Exodus 19:5-6:

Now therefore, if you obey my voice and keep my covenant, you shall be my treasured possession out of all the peoples. Indeed, the whole earth is mine, but you shall be for me a priestly kingdom and a holy nation. (italics added)

And this statement in Isaiah 56:7:

For my house will be called a house of prayer for all nations.

And especially these words of God to Abraham:

All peoples on earth will be blessed through you. (Genesis 12:3)

and:

Through your offspring all nations on earth will be blessed. (Genesis 22:18)

Therefore, like members of the Catholic Church, those who follow Swedenborg's theology do not think of the Hebrews, Israelites, or Jews as being God's chosen people in any exclusive way, but rather view Israel as a sign and representative of God's broader church, which includes people of all nations who worship God, and specifically those who worship Jesus Christ as God and live by his teachings.

This representative and symbolic nature of the ancient Israelite worship and code of laws is taken up and expounded in the Epistle to the Hebrews in the New Testament.

On the first point above, that Israel was chosen based on Abraham's belief in God, though not entirely rejecting that view, Swedenborg's theology goes in a rather different direction.

First, it is important to realize that although the initial promise was made to Abraham, he became the father of many nations, only one of which became God's chosen people in the Old Testament narrative. See my answer to the question, "Why is the Nation of Israel called Israel and not Abraham?"

That one nation was named "Israel," after the name given to Jacob by an angel of God in Genesis 32:28. In Swedenborg's exegesis of the narrative of the book of Genesis, the story in which that new name was given provides the key to why Israel was chosen over other nations. Here it is:

That night Jacob got up and took his two wives, his two female servants and his eleven sons and crossed the ford of the Jabbok. After he had sent them across the stream, he sent over all his possessions. So Jacob was left alone, and a man wrestled with him till daybreak. When the man saw that he could not overpower him, he touched the socket of Jacob’s hip so that his hip was wrenched as he wrestled with the man. Then the man said, "Let me go, for it is daybreak."

But Jacob replied, "I will not let you go unless you bless me."

The man asked him, "What is your name?"

"Jacob," he answered.

Then the man said, "Your name will no longer be Jacob, but Israel, because you have struggled with God and with humans and have overcome."

Jacob said, "Please tell me your name."

But he replied, "Why do you ask my name?" Then he blessed him there.

So Jacob called the place Peniel, saying, "It is because I saw God face to face, and yet my life was spared."

The sun rose above him as he passed Penuel, and he was limping because of his hip. Therefore to this day the Israelites do not eat the tendon attached to the socket of the hip, because the socket of Jacob’s hip was touched near the tendon. (Genesis 32:22-32)

This story, traditionally seen as the story of Jacob wrestling with God, but generally interpreted as Jacob wrestling with an angel, provides the key to why the descendants of Israel--as he was named by the angel in this story--became the chosen people through whom the Biblical narrative of the Old Testament was written, and ultimately among whom Jesus Christ, the Messiah (as Christians believe), was born.

In this narrative, it is not Jacob's belief, but his stubbornness and persistence in wrestling with the angel and not letting go until he receives a blessing that earn him the blessing of the angel embodied in the new name "Israel."

In fact, the Hebrew name יִשְׂרָאֵל (Yisra'el), "Israel," is composed of two Hebrew words, שָׂרָה (sarah) "to be a leader, commander," but also "to fight," and אֵל ('el) "God." So "Israel" traditionally means "soldier of God" or "prince of God," but in the context of its origin story it means, "one who fights with God."

Swedenborg's commentary on this story is far too extensive to reproduce here. It is contained in his massive work Arcana Coelestia (Secrets of Heaven) #4272-4317. Here are some key points based on his exegesis there and on various statements elsewhere in his theological writings:

As a stubborn and stiff-necked nation (see, for example, Exodus 32:9-10; 33:3-6; 34:8-9), the nation of Israel was well suited to:

1. Cling persistently to the new, monotheistic religion in a polytheistic world, and yet,
2. Continually violate that religion and its commandments in order to serve as a symbol and representation of how all people forsake God and violate God's commandments.

Contrary to the conventional wisdom that the ancient Israelites were chosen by God because they were an especially spiritual people, Swedenborg states that they were chosen specifically because they were a very materialistic people.

Precisely because they were not motivated by spiritual considerations, but primarily by material-world considerations such as wealth and power and the loss of them, they could be led by material curses and blessings, promises and punishments, to adhere to a monotheistic religion, against all of the pagan and polytheistic nations that surrounded them. (For more on this, see my answer to the question, "What did salvation mean to the Israelite people of the OT?")

In this way they could become a religion that symbolized and represented in outward form ("a copy and a shadow," in Biblical terms--see Hebrews 8:5; 10:1-2) the spiritual qualities of a truly spiritual religion that worshiped one God and followed God's commandments willingly from the mind and heart. Based especially on the Epistle to the Hebrews, Catholics, and most Christians generally, believe that Christianity is that truly spiritual religion prefigured by the ancient Israelite nation and religion.

Back to the narrative of Jacob wrestling with the angel, it was Jacob's stubborn persistence in clinging to the angel, even after being injured, until the angel blessed him that earned him the blessing of the name "Israel," which became the name of the nation that was God's chosen people in the Old Testament narrative.

Based on this, Swedenborg states that it was the ancient Israelites' insistence that they should become the chosen people that secured that position for them in preference to any of the other nations descended from Abraham (or, for that matter, any other nation, Abrahamic or not) that could have become the chosen people.

As an example of this, consider the stubborn, persistent, and rather wily character of Jacob in comparison to his brother Esau--who, as the elder brother, should rightfully have become Isaac's heir. This contrast of character is seen clearly in the story of Jacob securing Esau's birthright in Genesis 25:29-34:

Once when Jacob was cooking some stew, Esau came in from the open country, famished. He said to Jacob, "Quick, let me have some of that red stew! I’m famished!" (That is why he was also called Edom.)

Jacob replied, "First sell me your birthright."

"Look, I am about to die," Esau said. "What good is the birthright to me?"

But Jacob said, "Swear to me first." So he swore an oath to him, selling his birthright to Jacob.

Then Jacob gave Esau some bread and some lentil stew. He ate and drank, and then got up and left.

So Esau despised his birthright.

In the context of the narrative, this story demonstrates that Esau, who was so lackadaisical about his birthright that he would sell it for a bowl of stew just because he was hungry, did not have the strength of character to become the one through whom the promise and the covenant would be given. Hence the proverbial saying, "selling one's birthright for a mess of pottage."

Jacob, by contrast, had a dogged and determined character that drove him to supplant not only his older twin brother, but anyone else who might have been an aspirant to the honor of being the particular patriarch of God's chosen people. And his descendants after him inherited that quality of stubbornness and persistence of character from him.

So in contrast to the Catholic view of Israel being chosen because of the faith of their patriarch Abraham, in Swedenborg's theology Israel was chosen due to the stubborn, persistent, and stiff-necked character of Jacob, or Israel, who was patriarch only of that particular nation, and not of any of the other nations that descended from Abraham.

As the Old Testament narrative unfolds, that stubborn, persistent, stiff-necked character accounts both for the greatness and for the downfall of the Israelite people. As such, they served admirably as the people through whom God could give the Bible, or Word of God, to humanity, and through whom Jesus Christ could be born into the world.

From the perspective of Swedenborg's theology, then, through these two contributions to humanity,

1. providing the human culture in which the Word of God was written, and
2. providing the human vessel and culture for the birth of Jesus Christ into the world,

the particular descendants of Abraham who were the ancient Israelite people did indeed become a blessing to all the nations.

Despite the differences about why in particular Israel was chosen, on these two points I think Swedenborg's theology is probably harmonious with Catholic theology, and with the theology of most other Christian denominations.