Installation view of Bruce Nauman's Human Nature/Life Death/Knows Doesn't Know, 1983, neon, 107 1/2 by 107 inches; at the Arsenale, "All the World's Futures," 56th Venice Biennale, 2015. Photo Gregory Volk.

In a time of considerable art world churning and froth, marked by endless proliferation and a high-octane market glutted with eminently saleable and collectible abstract paintings by young stars (many of them male, white and from the West), Okwui Enwezor's compelling 56th Venice Biennale exhibition "All the World's Futures" is a welcome corrective—a shot across the bow. Spanning the vast Arsenale and the ample Central Pavilion at the Giardini, with several works installed outdoors in the Giardini, this complex, tough-minded exhibition decisively shifts focus from the art world to, well, the world. Contact with the world is the prevailing theme, revealed in works that address crises and wars, race relations and enduring racial strife, resurgent capital and shocking economic disparity—all defining characteristic of this tense, fraught era. Eschewing frivolity and fun, as well sexiness and even joyfulness, this show is serious, sober, unstinting, moral, critically engaged with pressing issues and occasionally fierce.

Enwezor establishes his intentions and the exhibition's tone at the outset, in the first room of the Arsenale. Algerian-born Adel Abdessemed's sweetly titled Nympheas (Water Lilies) (2015) is anything but sweet. Large knives, stuck in the floor, form bristling bouquets that exude conflict and danger. On the walls are several of Bruce Nauman's colorful neons, including Raw War (1970), which features the word "WAR" in flickering neon tubing. This piece was made during the height of the Vietnam War, and it transforms a colorful advertisement into an investigation of language as well as a meditation on violence and upheaval. Human Nature/Life Death/Knows Doesn't Know (1983), with the words in the title flashing on and off in different sequences, also fits the current climate marked by wavering hopefulness and prevalent anxiety.

Speaking of a shot across the bow, many works in the Arsenale incorporate and transform weapons or destructive objects of some sort. The Propeller Group, a Vietnamese collective established in 2006 by Tuan Andrew Nguyen and Phunam Thuc Ha, presents The AK-47 vs. The M16 (2015), named after the most famous Russian and American rifle, respectively. In an ultra-high-speed video and a transparent ballistic gel block, you see how two bullets shot from the rifles collided and fused, a crash at once frightening and spectacular. Monica Bonvicini's black, impacted sculptures, suspended from the ceiling on chains, are made of chainsaws cast in concrete and then covered with black liquid rubber. Part reconfigured S&M fetish gear and part transformation of the tool, with their ultra masculine connotations, Bonvicini's willfully rough sculptures are surprisingly elegant.

Hiwa K collected and melted down military ordnance like bombs, bullets and artillery shells found in his native Iraq, where there is no shortage of such stuff—to date, he has identified weapons supplied by some 30 countries. The material was formed into a large bell that can't be rung because it sits directly on the floor (The Bell, 2014-15). An accompanying two-channel video depicts the process and also recounts stories of war. Suggesting both a warning and a call to prayer, Hiwa K's bell quite literally turns destruction into creation.

The gun isn't visible, although it is crucial, to Steve McQueen's haunting and elegiac two-channel video Ashes (2014-15). On one side of a screen, footage from 2002 shows a young and carefree Grenadian fisherman perched at the end of a boat bobbing in the sea. McQueen met the young man while working on a different project. On the other side of the screen, meticulous, talented craftsmen carve the young man's gravestone for his reburial (he was formerly buried in an unmarked grave) while a soundtrack features two friends telling what happened: the young man found drugs on the beach, was later accosted by drug dealers, and shot multiple times. McQueen's consternation and sadness is palpable, while this story of a life eclipsed by power, money and rampant violence connects with many other stories elsewhere.

Among other standouts is Chinese artist Cao Fei's enthralling yet hard-hitting La Town (2014). Elaborate tabletop sculptures, including fabricated landscapes, buildings and tiny figurines, are the analog things the artist used to make her video of a dystopian future city rife with discord, violence, strip club entertainment, decaying infrastructure, ecological mayhem, demonstrations and police raids, but one that also displays moments of sheer loveliness. Ibrahim Mahama, from Ghana—one of numerous African artists in the exhibition—covered the two sides of the outdoor corridor with brown fabric expanses coarsely woven from jute fiber sacks, commonly used in Ghana's open air markets for trading of commodities like cocoa (Out of Bounds, 2015). Displaying the names of owners, companies, and products, Mahama's impressive, space-altering work is like an architectural skin or a living organism, bearing signs of Ghanian commerce, globalization and labor, including frequently exploited migrant workers. Back indoors, German Katharina Grosse's painting installation Untitled Trumpet (2015) is a marvel of sweeping, bright, spray-painted colors mixing with objects and materials, including draped fabric, mounds of soil and aluminum parts. It's an enveloping, transformative, even ecstatic work but with a rough streak, hinting at landslides, entropy, and environmental disaster.

The Arsenale, as I wrote, is vast, but it's well worth venturing all the way to the end, to the garden and remote exhibition spaces there. You'll find riveting videos, which are regularly released on Vimeo, by the Syrian collective Abounaddara. Without any commentary or obvious ideological agenda, these remarkable shorts let diverse Syrians—instead of the biased international media—tell what is happening to and with them during an unimaginable crisis. Several people reveal how they avoid (or try to avoid) aerial bombardment, and a single courageous woman, a teacher, recounts how she staged her own protest against ISIS in an ISIS-controlled area. Among the several components in Sarah Sze's enchanting mixed media installation The Last Garden (Landscape of Events Suspended Indefinitely) (2015) is a hammock-like structure made of rich blue nylon strands strung between two trees. It displays colorful bits of acrylic paint while a piece of rock or brick, suspended on a string, dangles just above. There is such beauty and grace here, yet everything is also unnervingly fragile and ephemeral.

At the Giardini, the Central Pavilion begins with two outdoor works. On the façade above the entrance, Glenn Ligon's neon blues blood bruise (2015), which replaces the longstanding "la Biennale" sign, is like a clarion call to deal with urgent matters, whether the violence of warfare and cultural conflicts or the police shootings of black men in America. Colombian Oscar Murillo's large black canvases that partially obscure the entrance feature oil, oil stick, thread and dirt. They are paintings but seem like flags, and strike a somber, funereal tone (signaling devices in now bastard territory, 2015).

The most emblematic and, for me, problematic work in the Giardini is an exhibition-long reading by actors (directed by Isaac Julien) of Karl Marx's Das Kapital. Obviously intended to highlight extreme income disparity (the infamous 1% and 99%) this public reading, billed as an oratorio, of Marx's classic text is another clarion call. Yet many people (especially Eastern Europeans who grew up under Communist governments) will recall that Joseph Stalin, emboldened by his understanding of Marx, slaughtered some 34 million to 49 million people; that Chairman Mao, likewise emboldened by Marx, was responsible for the deaths of about 45 million; and that all sorts of authoritarian regimes, including the former East Germany with its notorious state security apparatus the Stasi, derived their abysmal power from Marxist ideology.

That aside, there are many treasures here. Ghanaian-born British artist John Akomfrah's unmissable three-channel video installation Vertigo Sea (2015) mixing archival and new material, is a remarkable meditation on nature, as it investigates our conflicted relationship with the environment. It is gorgeous, sublime, and oftentimes harrowing, and should be seen in its entirety, probably at least twice.

Astute and creative curatorial decisions abound in this building. Isa Genzken's architectural sculptures atop pedestals, many from the 1980s and ‘90s, look just great paired with Walker Evans's photographs from his 1936 series "Let Us Now Praise Famous Men," some of which also feature houses. Isaac Julien's two-channel video Capital, 2013, shows an illuminating discussion centered on capitalism, between himself and American Marxist scholar David Harvey, with arresting shots of the obviously well-heeled audience factoring in. It's perfectly paired with Rirkrit Tiravanija's many "Demonstration Drawings," (2006-15), for which Tiravanija commissioned Thai artists to make drawings of worldwide demonstrations (some against economic injustice) based on photographs in the International Herald Tribune. American Ellen Gallagher's new paintings harmonize in a room with upright figurative sculptures by Pakistani-American Huma Bhabha and the Australian Aboriginal Emily Kame Kngwarreye's quietly pulsating, reverential abstract painting Earth's Creation (1994).

There aren't that many Americans in the exhibition (which is fine), and many that are included are African-Americans (which is superfine). This show includes an ample number of black artists from Africa and the African diaspora, no doubt a record for the Biennale. Kerry James Marshall's loosely Rorschach blot-like colorful paintings, blending abstraction and representation, and his figurative paintings of African-Americans are especially striking.

As with Bruce Nauman's neons at the Arsenale, Enwezor's inclusion and recontextualization of Robert Smithson's Dead Tree (1969/2015) is an excellent curatorial touch that teases fresh meaning from this seldom seen work. An approximately 35-foot-tall uprooted tree, fitted with several double-sided mirrors, lies on the floor. It's been radically displaced and subjected to abrupt upheaval, yet still has power, and it embodies the kind of thoughtful contact with the world that courses through the rest of this exhibition.