It is undoubtedly a vast topic, and of utmost importance to all human beings. The magnitude of this topic's importance is such that almost no human being is left untouched! The issues involved, cannot, in all honesty, be adequately treated to, in a single article. This piece must therefore be regarded as a very brief glimpse at the issues.

A curse has been defined as a "solemn utterance intended to evoke a supernatural power to inflict harm or punishment on someone or something" (Oxford Dictionary). Another definition closely mirrors the first: "A prayer or invocation for harm or injury to come upon one...an imprecation."

Curses may be executed by: (i) Elohim/God; (ii) parent(s); (iii) or one senior to the curse's recipient, and; (iv) by one in authority over the recipient. Additionally, curses may be self-inflicted.
Curses may be uttered over a person, a family, a clan, a tribe, a nation, a place, a city or town, a building or an object such as a tree (remember Yahshua and the unfruitful fig tree).

Curses are largely responsible for much of human suffering today. Our father Adam, was created perfectly. The environment in which he lived was perfect and beautiful. The statement; "...and God saw that it was good", is a frequent refrain punctuating the entire Creation Week in Genesis chapter one. However, in the course of time, sin crept into the perfect setting of Eden via human disobedience to the voice of Almighty God. As a result, the ground was cursed into malignancy a fact of which we are all witnesses today. Secondly, the female gender also received a curse in matters of childbearing. In sum, the violence, bloodshed, disease, drought and famine, floods, earthquakes, volcanoes, storms, and hurricanes along with other natural disasters are all the effects of a world whose ecological equilibrium has been negatively affected by the divine curses as outlined in Genesis 3:14 - 24.

In Genesis 12:1-3, we see God declaring that whoever curses Abraham will find himself under a divine curse. Fast forward to the early 20th Century and we see an example of this word coming to pass. 
It is the beginning of the Second World War. Germany's Adolf Hitler is hell-bent on implementing his "Final Solution to the Jewish problem." He is busy carting off millions of distraught Jews in Nazi-occupied Europe to his concentration and extermination camps deep in Poland and Germany. The American ambassador to the United Kingdom, Joseph Patrick Kennedy is in a good position to help the hapless Jews escape Nazi tyranny and find new lives in America. He flatly refuses to do so and in fact, goes to the extent of preventing an overloaded Jewish refugee ship from docking in any of America's harbors!
In the course of the War, his firstborn, ace pilot Joseph Patrick Kennedy Jr, is shot down during an air-raid mission over Nazi-occupied Europe.
The ambassador's second son, John Fitzgerald Kennedy, a PT boat captain in the US Navy, has his  vessel sheared in two by a Japanese destroyer in the Pacific. JF Kennedy later becomes president, but scarcely three years later, is assassinated on the streets of Dallas, Texas. The fateful day is the 22nd of November,1963. The third Kennedy scion, Robert F Kennedy is similarly assassinated as he campaigns for president in 1968. Other members of the Kennedy clan have suffered air and motor crashes, mental illness, drug addiction, various scandals etc. Even to the casual observer, the evidence as to the operations of a curse in that famous American dynasty seems to tip the scales. Could the Kennedys be victims of the divine curse in Genesis 12?

Then there is the case of Ishmael and Esau. Right from their childhood, relations between Ishmael and his brother Isaac (the son of promise) were decidedly frosty. In fact, the upshot of that was the fact that both Ishmael and his mother Hagar had to be sent away from Abraham's household (Genesis 21:4). God's angel had already indicated that Ishmael would be; "...a wild donkey of a man..." and that he  would "...live in hostility toward all his brothers." (Genesis 16:11-12).

Matters were however escalated for the worse when Rebekah (Isaac's wife) begot the twin boys, Esau and Jacob (Genesis 25:21-26). Esau married Canaanite women, Judith and Basemath, without a parental blessing. It was a thorny issue that brought much grief to his mother Rebekah. Esau then tried to make amends by seeking another spouse from his uncle, Ishmael. He was therefore wedded to Mahalath, one of Ishmael's daughters. So the Ishmael-Esau bloodlines came together and formed the trunk of the genealogical tree of the Arab peoples as we know them today. 
The fact that Jacob tricked him out of his birthright, and later stole his blessing as firstborn, never sat well with Esau. He secretly nursed a grudge and vowed to eliminate his twin brother once their aged father died (Genesis 27:41). So we see that not only did Ishmael begrudge his brother Isaac the favored "son of promise" status, but that Esau too, harbored a grudge against Jacob over the birthright issue. The Bible is on record that this long-standing grudge has never been forgotten. Says the prophet Ezekiel:

"... because you HARBOURED AN ANCIENT HOSTILITY and delivered the Israelites over to the sword at the time of their calamity..." (Ezekiel 35:5, NIV, full caps mine).
    And; 
"...because the Philistines (present-day 'Palestinians'?) acted in vengeance and took revenge with malice in their hearts, and with ANCIENT HOSTILITY sought to destroy Judah..." (Ezekiel 25:15, NIV, brackets and emphasis mine).

Because of the foregoing, the prophet Isaiah describes Edom/Esau as "...the people of my CURSE..." (Isaiah 34:5).

Today the Arabs continue to oppose Israel's existence despite occupying over 13 million square kilometers of territory (spread over 22 countries) while Israel has a paltry 28,000 square kilometers sliver of territory!

A cursory glance at the Arab world today makes one wonder whether the above curse is not in effect already. Syria, Yemen, Libya, Iraq and Lebanon are on the brink of ruin via debilitating civil wars. The Middle East remains one of the most troubled neighborhoods in the modern world. The prophet Obadiah intimates that the end result of the above curse will be the total annihilation of the House of Esau. He says: "...there will be NO SURVIVORS from the house of Esau..." (Obadiah 18, NIV, emphasis mine).