• US manufacturing activity accelerated in May to its strongest level in four years.
• The flash manufacturing Purchasing Managers' Index rose to 55.3 in May.
• Companies increased inventories to protect against supply disruptions and rising costs.
• The conflict with Iran has disrupted shipping and pushed up energy prices.

This expansion may indicate that US manufacturers are preparing for prolonged supply chain disruptions, which could have significant implications for the global economy. The focus on building safety stocks suggests that companies are taking a cautious approach to managing risk, which could impact their ability to respond to changing market conditions.