The annual pilgrimage to Mecca known as the Hajj, which observant Muslims are supposed to make at least once during their lives, officially begins on August 19.

Mecca is located in Saudi Arabia, which is currently embroiled in serious disputes with Muslim nations such as Qatar, Iran, and Yemen, as well as Western countries with Muslim citizens who wish to make the pilgrimage, most notably Canada.

Canadian Muslims are reportedly anxious about making the trip to Saudi Arabia, in some cases canceling travel plans and postponing their pilgrimages until relations between the two countries improve. The Saudi national airline suspended service to Toronto this week, among other measures taken against Canada. Prospective travelers to Saudi Arabia are worried the situation could grow even worse during their journey. In fact, some Hajj pilgrims who left early are uncertain how they will get home, as other carriers may not have enough seats to handle displaced Canadian passengers from the Saudi state airline.

The dispute began when Canadian Foreign Affairs Minister Chrystia Freeland criticized Saudi Arabia’s detention of social activists. The Saudi Foreign Ministry considered her remarks “an attack on the Kingdom of Saudi Arabia” and the independence of its judiciary. The conflict swiftly escalated to the point where neither side seems likely to apologize or back down in the near future.

Iran is at odds with Saudi Arabia for numerous religious and strategic regions. The Saudis banned Iranians from the Hajj in 2016 but then invited them to return in 2017.

The Iranians want custodianship of the holy cities of Mecca and Medina to be taken from the Saudi government, charging the Saudis with politicizing the pilgrimage, interfering with the practice of Shiite Muslim rituals, and doing a generally poor job of providing for the safety and comfort of visitors. Iranian Supreme Leader Ayatollah Ali Khamenei in July pointed to the deadly 2015 stampede in Mecca, which killed up to 2,400 people, as enduring evidence of Saudi mismanagement.

Saudi Arabia and its allies in the Gulf Cooperation Council have imposed a blockade on Qatar since June 2017, accusing Qatar of supporting terrorism, seeking to destabilize other governments, and making common cause with Iran. The number of Qataris making the Hajj journey to Saudi Arabia dropped from 12,000 in 2016 to less than 70 in 2017.

Qatari media has reported virtually no one from Qatar will participate in the Hajj this year, angrily accusing the Saudis of politicizing the religious event by denying them visas. France24 noted on Wednesday that at least one Saudi newspaper closely aligned with the royal family explicitly stated that Qataris must “either choose God’s house of the Hamads,” meaning the rulers of Qatar.

“It is necessary for the Qataris to move to free themselves from a regime that does not respect our religion, does not care for the rights of its citizens, and ceases to intervene, conspire, indulge in illusions and support and finance terrorism,” the Saudi paper Okaz wrote on August 9.

The Saudi Ministry of Hajj insists Qataris will not be denied passage and accused Qatar’s government of deliberately misleading its people to increase tensions. The ministry pointed out that Qatar blocked two different websites created for Qatari citizens to apply for Hajj visas. The ministry’s last statement on the matter invited Qataris to come by any means except Qatar’s banned national airline and promised visas would be arranged upon arrival.

The Saudi government sets visa quotas for various countries to control the size of the crowd in Mecca, especially while several years of renovation work proceed on the Grand Mosque. Critics say the quota system is corrupt and politicized.

25,000 pilgrims from Yemen have been invited to the Hajj this year, even though the Saudis are deeply involved in the long and brutal civil war between Yemen’s internationally recognized government and Houthi tribal insurgents supported by Iran.

The Saudi ambassador to Yemen stated in July that pilgrims would be accepted “whether they come from areas under the legitimate forces or other areas under the control of the Houthi militias.”

The Yemeni government warned on Thursday that Houthi militia forces are obstructing Hajj pilgrims from entering Saudi Arabia and seizing their passports.

Some Iranians have criticized their government for allowing pilgrims to visit Mecca this year, and even offering them a subsidy worth about $200 because they believe Saudi Arabia will divert income from Hajj tourism to finance its war effort in Yemen. There is also some grumbling on Iranian social media about Tehran spending money to subsidize the Hajj while the national economy is collapsing in the wake of American withdrawal from the Iran nuclear deal.

All told, at least two million visitors are expected for Hajj 2018, and some estimates put the number closer to three million. Many of the visitors come from impoverished and conflict-ridden countries, raising concerns about security and the ability of Muslims from poor countries to afford food and shelter during the sometimes grueling and extremely crowded pilgrimage.

The Hajj route is now equipped with thousands of communication towers and wifi hotspots, and there is a “Smart Hajj” app to guide visitors. The app monitors the location of each pilgrim and can be used to summon emergency or special needs assistance as needed.

The National provided a concise explanation of how the Mecca (or Makkah) stage of the Hajj works:

Muslims follow the actions of Prophet Mohammed when he performed his Hajj in 632 CE. Those accompanying the Prophet observed his every move and these steps are performed in the same sequence today. Before beginning Hajj, pilgrims must enter what is known as a state of Ihram, whereby they prepare their bodies and mind for the rituals ahead. This requires them to recite an intention and adhere to a certain dress code. Men must wear garments without stitching and cannot cover their heads, while women can wear stitched garments but cannot cover their face. After entering Ihram, pilgrims begin their Hajj from the Kaaba, the holiest site in Islam as it holds the Masjid Al Haram, a structure in the middle of the Kaaba that Muslims believe was placed by prophet Ibrahim thousands of years ago. As they approach the Kaabah, pilgrims must circumambulate in a counter-clockwise direction, meant to express the devotion of Muslims praying to one God. They must then perform Sa’ey, whereby Muslims re-enact the journey by Hagar, the prophet Ibrahim’s wife, as she went between two small hills in Makkah, Al Safa and Al Marwa, looking for water for her son Ismail. Muslims pace between the two points, in remembrance of the miracle whereby God caused a spring to well up from underneath an exhausted Hagar. It is today the Well of Zamzam.

This is the stage of the pilgrimage that causes so many logistical and safety problems for the Saudi government because so many people are moving through narrow streets and the relatively small square around the Kabaa. The symbolic stoning of the Devil in Mina, which is about two miles away, was the site of the 2015 stampede.

A crane working on the Grand Mosque collapsed in September 2015 and killed 111 people. Another crane collapsed at the mosque just a few months ago, but no one was killed in the latest incident.

Despite the overcrowding concerns and international tensions, Al-Arabiya reported on Thursday that a “sense of calm” hung over the airport in Riyadh as the first waves of pilgrims arrived. Saudi ministers said they have provided over 17,000 buses to transport visitors, constructed a network of tourist information centers, and organized a volunteer assistance program. Tent cities have been erected to house the enormous number of pilgrims.